How to Install a Transmission Cooler on a 2005-2008 Pontiac Grand Prix GXP

(a useful guide for other LS4 vehicles or 2004-2008 Grand Prix cars as well)

Disclaimer

If you follow my instructions, you’re doing so at your own risk. By proceeding to follow anything I have written below, you agree to hold me without liability. The guide below is simply how I did it on my GXP.

If you found this guide helpful and would like to make a donation to me for my dozens of hours of time and effort writing this guide, providing photos and diagrams, and creating a website for it, you can donate via this PayPal link. Please throw me at least $5 if you followed this guide.

To help make things easy for you, I've also linked to the products I've mentioned with Amazon links when possible.

Why did I decide to spend hours and hours of time writing this and building a website?

I don't want Grand Prix GXPs and other LS4 cars to disappear just because there's very little online DIY help. I'm a major 4th generation Camaro enthusiast, and the resources for DIY online are still significant to this day, which makes me sad for the GXP owners. I wanted to do my part in helping keep these GXPs and other LS4 cars on the road by creating something other owners could follow in order to prolong the life of their cars.

I created this “how to install a transmission cooler on a Pontiac Grand Prix GXP” guide because I was frustrated by how few resources were still available online in 2021. If you aren’t aware, Photobucket pretty much killed forums by ruining what used to be very dependable FREE photo host everyone could count on for over a decade. The most popular "how to" guide I ever found a reference to was hosted on Photobucket and it's now completely gone from the internet. Some of the other existing “how to” guides that aren’t crippled by dead photos and dead links use one of the specially made coolers made by Triple Edge Performance that they no longer make and sell or are YouTube videos that I didn't find useful at all. Overall, looking at these guides created nothing but confusion for me, as I couldn't really find a guide to what parts or tools were needed, nor a useful step-by-step walkthrough, so I decided to create my own guide after spending a ton of time researching... planning... and finally installing. I’m almost embarrassed to say it… but I researched the parts necessary for this job plus what I could learn about the procedure for more than 20 hours and I still didn’t have enough info to be comfortable getting started. The info remaining online in 2021 was/is truly underwhelming. I ended up consulting my factory service manuals to try to piece together what needed to be done. Naturally, this is not a process covered in those, because this is purely an aftermarket improvement to the car. The process required some creativity.

Introduction

I've owned my 2006 GP GXP since January 2009. I love this car and I still treat it like a $35k car all these years later. I'm a bit of a perfectionist and I did not want to poorly mount my cooler or tear up my car unnecessarily in the process. In my research, I saw all sorts of hackjobs held together with zipties by other people who were doing their best, but just didn't know what else to do because a guide didn't exist. I wanted to do a really good job, so I enlisted the help of my father, a retired engineer, who has been working on his own cars since before I was born.

This isn't my first time working on a car, but I don't do it for a living either. I wanted to write this guide in a detailed way that even fairly inexperienced DIY car owners could follow it and do a beautiful job. Would I recommend you do this job if you've never worked on a car in your life? Absolutely not! A detail-oriented newbie with tools could most likely finish mounting the cooler successfully though. The actual plumbing work is the part a newbie probably shouldn't do—my dad did the bulk of the plumbing, because I had no experience with doing it.

Note: If you own an Impala SS, Monte Carlo SS, or Buick LaCrosse Super with a factory installed LS4 V8 engine and 4T65-E transmission, you might find these instructions very useful as well. For the people with 2004-2008 3800 V6 Grand Prix cars… some of these instructions will be useful for you, but I’d have to think that the cooler I am suggesting is overkill for those smaller engines. I've never owned a V6 Grand Prix, but I know you guys don't run nearly as hot as the GXP cars. The routing of the transmission cooler lines to the radiator is also different on the V6 cars (it's pretty much mirrored).

How much time should you budget for this process?

If it's not hot outside, you could do this all in 1 day. It would be smart to consider this a 2-day weekend project though.

Tip: if you mount the cooler the same way we did, as long as you don't attach the brass barbed fittings, I bet you could just mount the cooler and put the car 100% back together. Then you could just handle the plumbing yourself another day when you have more time, or drive it to a transmission shop for them to plumb it for you.

The completed install. My Tru-Cool 40k transmission cooler is visible behind the bottom grill if you look hard enough at it.

Considerations for selecting your transmission cooler

Look… this is all just my opinion based on the hours of research I did (based on other people’s opinions and experiences) and not based on any scientific data (unfortunately). I’m just giving you my opinion. Take it for what it’s worth.

The LS4 cars run really hot for many reasons. Discussing those reasons isn't within the scope of what I want to accomplish here, but our transmission fluid gets up to 200 degrees very quickly compared to the V6 Grand Prix cars and other cars in general. Temperatures higher than 200 are bad for the fluid and then bad for the transmission.

There are three main types of transmission coolers

1. Tube and Fin Coolers – cheap, small, and don’t do too much. Probably a waste of time unless you live in the far northern US or Canada and only barely run hot. I’m pretty sure they’re 100% useless in my part of the US (Texas).

2. Plate and Fin Coolers – looks like a little radiator, too small to run as a standalone cooler, still kind of inexpensive. Probably pretty decent if you live in Chicago or somewhere fairly far north. Probably very good and easy for plumbing inline without a lot of work. (The Hayden coolers I've seen are this type).

3. Stacked Plate Coolers – range from big to huge, most efficient type, can be ran in a standalone configuration with or without a bypass. These are what southern US people need to use. These are so big that you absolutely HAVE TO take off the front bumper (it's such an easy task too...). (The Tru-Cool 40k is one of this type of coolers).

Refer to Transmission Cooler: The Definitive Guide for even more details. Some of these coolers have fans on them, but I didn’t need one with a fan, so I didn’t care to know more.

Think about where you live, where you drive, and how you drive

I live in Texas (Dallas area) where it’s generally between 30 and 115 degrees Fahrenheit outside. I park my car in the garage when it is at home, so the lowest temperature the transmission fluid will be in winter is around 40 or 50 degrees when at home. The car has tended to stay warmer than outdoor temperatures by the time I leave work, so I don’t ever expect to see (for example) 20 degree transmission fluid. I mostly use my car as a daily driver to commute to work and go shopping. We don't use it for road trips, and I don't own it for racing. I accelerate more quickly than most people, but not like my hair is on fire. I'm not an Uber driver... I don't deliver pizzas... I usually drive 15 to 30 minute trips.

I’m not going to run through all of the possible configurations and help you pick a size no matter where you live, but I do have some thoughts to share. If you live in a part of the US where you never see 110 degrees, but you’ll see up to 90 degrees often, you could (and possibly should) install a Tru-Cool 30k cooler instead. The 30k ones have the inlet and outlet on the side (instead of the bottom like the 40k), and that would help a LOT with the installation. I don’t know how they perform, and I’m not sure if someone in my environment could successfully use a 30k standalone in the Summer or not, but from the aspect of plumbing the thing to your transmission on your GXP... I wish I could have gone with one of them. If you live in a northern part of the US that actually does get below 30 degrees every year, then you’re going to have a tougher decision to make. Do you run the cooler standalone, but plumb in a bypass? Do you risk running a cooler standalone and have really, really cold transmission fluid the first few miles you drive the car? Do you plumb one inline just to help out the factory one that goes through the radiator? You’ll have to figure this out based on your own situation, do some research, and just kind of guess and hope you’re right.

I chose the largest of all transmission cooler options, and ordered a Tru-Cool Max 40K (LPD47391) from Oregon Performance Transmission. It's a popular choice for running standalone on these cars.

I know nothing about plumbing transmission coolers inline, but I do know that if I lived in the northern US doing my exact same line of work (an office job)... and the highest temperature I’d see in the summer was 85 degrees… I would just buy a Plate and Fin cooler and run it inline. However… if I was an Uber driver in the same northern environment… I’d go more heavy duty and do a large Stacked Plate cooler and plumb in a bypass. You’re really going to have to think about how you use your car and how cold and hot it gets where you live.

Let’s get down to business regarding the installation of a Tru-Cool 40k now. This is a HUGE cooler, so if you're installing a smaller one, you will have less work.

Why should an owner do this? Why not just take the car to a transmission shop?

I have two major reasons. One, I'd never pay someone the huge number of labor hours to put in this many hours of time into carefully disassembling the car and engineering a high quality solution to mounting the huge cooler. Two, you're incredibly unlikely to find someone who is going to spend all day on your car and put in an enormous transmission cooler. If you just want to pay a transmission shop to put in a small inline cooler, they'll probably just take out your driver's side headlight and slap one in with some zipties and you'll see a tiny bit of benefit. So if you're handy... install the cooler yourself. Pay a professional to do the plumbing if you want, but spend the time doing the time-consuming, rather easy, work yourself.

Will a transmission cooler fix my failing transmission?

No. Ideally, we all should have installed transmission coolers when the cars were brand new. I put it off for a decade because I lived only 3 miles from my job for most of that time period, so I'd rarely ever see higher than 180 degrees. A transmission cooler isn't going to fix your burnt up transmission if you've been driving repeatedly at 220 degrees pretty much every day. Fluid and filter changes every 20 to 25 thousand miles will help, but not very much if you've been cooking your transmission constantly.

Also, for your information, DEXRON VI automatic transmission fluid is pink/red. It doesn't change color to tell you it's wearing out (mine at 21,000 miles still looked brand new in color). It changes color in response to too much heat. If your fluid is brown or black, it's been burnt. If you're seeing burnt fluid, your transmission probably isn't doing so well anymore either. It might be a bit late for trying to save it. But if you intend on keeping the car, go ahead and do this ~$200 mod and start saving up for a new transmission that hopefully won't ever see incredibly high temperatures like your current one.

Tools and Parts

I’m going to give separate lists, because some of you may want to mount the cooler a little differently or plumb it a completely different way.
My disassembly instructions are based on the service manuals (shop manuals) as much as possible.

Tools for disassembling the car

Steps for disassembling the car

Note: scroll down to see photos I took during this process. Sometimes I refer to a photo in the steps below, but it's at the very end of these steps instead of near the text.

1. Use your regular size ratchet and a 13mm socket to temporarily remove the 3 bolts from the passenger side bar that is over the battery. You technically just need to move this bar enough that you can access the negative battery post on the battery. Use a 10mm socket to remove the bolt securing the negative battery cable. If you are like me and have the interesting “lock” for that cable, pay attention to the way the polygonal pieces of metal are stacked once you have removed the nut and those two polygons. (Take a photo of it. Unscrew the screw and remove the triangles. Wiggle the bolt out from underneath the T-shaped piece. Slide the T-shaped piece out.) Lift the negative battery cable off the post, push it out of the way, and reassemble the lock and such but put it on your workbench out of harm’s way. You can reattach the bar with the 13mm bolts for now if you want, because you won’t need to remove it until you’re hooking the battery back up much later.

2. Remove both headlights. They are secured to the car by a black piece of metal with a single 10mm bolt in it. You remove that bolt, pull the metal piece upward, and then slide each light straight out toward yourself. If the metal piece won't slide upward, try wiggling a little or moving things a millimeter here and there. If it won't budge, spray it with some silicone lubricant and pry it with one of the plastic pry tools. A tiny bit of wiggling may be needed to slide the headlamps out, but they come straight forward. Once you have the headlamps slid out, you’ll need to detach the black and purple electrical connector. This connector is difficult the first time you ever encounter it, but it is so, so simple. Very close to where the wires enter the connector there is a square tab that you need to squeeze gently with your thumb to remove the headlamp. It will surprise you how simple it is once you squeeze the correct portion of it. The connector is impossible to remove without discovering that tab. After you’ve removed the headlamps and set them aside, you can replace the 10mm bolts and tighten them finger tight so you don't lose them.

3. You're almost ready to lift the car now. Make sure the transmission is in Park... set the parking brake with your left foot... and put some small wood blocks behind your rear tires. If you have a floor jack similar to mine, there is a boxed metal subframe under your GXP and you need to get the jack exactly centered on that before lifting. (Reference "jacking instructions" image). The shop manual warns about potential damage if you lift the car from here without being centered. You slide your low profile floor jack in perfectly centered from the front and get the saddle of the jack centered on that piece of silver colored metal. If you own a scissor jack you’ll have to refer to your car’s owner’s manual and lift behind the wheels on the specific jacking locations.

4. Our cars don’t have great locations for placing jackstands, but they are essential to safely suspending your car in the air. Ideally, you need to put them to where they can grab around something so the car is less likely to slip off. There’s a good weld on the box subframe that is good for this on both sides. I didn’t use it until my second time lifting the car so… look at what I circled on the photo instead of doing what I did. What I did made it possible for the car to slip off, so I left the jack under the front of the car for extra security, which isn't as ideal as doing it safely.

In case my photo doesn’t work someday… finding the driver’s side jackstand location is easy. It’s a big piece of metal welded onto the outer edge of the box frame very close to the transmission pan. The passenger side one is in the same location on the opposite side of the car.

5. Remove the front fender liner bolts (reference "front fender liner removal" photo) using a 7mm socket or 9/32 socket. You don’t need to remove the wheel if you use sockets, but you will if all you own is a socket driver in this small size. There are 9 of these bolts on each inner fender liner. The bolts are not absolutely identical. If you have the front passenger side wheel directly in front of you, the order from left to right is:

big washer, regular, regular, regular, regular, regular, shorter screw, big washer, big washer

The shorter screw goes onto the engine compartment (frame rail). The bigger washer ones are all mounted really low on the inner fenders in front and behind the tires.

6. Remove the four 7mm bolts on the bottom of the front bumper (reference "removal of retainers from lower front bumper" photo if you need to (you probably won't need to)). Remove the 6 pop fasteners using your plastic prying tool. (You can use a flathead screwdriver if you don't want to buy one of these... but these plastic prying tools are amazing, make the process so much easier, and don't bend/damage the pop fasteners like a screwdriver will...). You pry up the head of the plastic nail and then pop the entire fastener out of the hole with your fingers.

7. There are three very obvious 10mm screws holding the lower air deflector to the bottom of the car (reference "lower air deflector removal" photo). Remove those. Some people call this lower air deflector the “rock guard”. Note: I don't know why people complain about how hard it is to remove this, it's absolutely simple if you know the next step.

8. The final step to removing the lower air deflector is to slide it off the plastic bolt that prevents the deflector from falling off and landing on your face once you've removed the 3 screws in the previous step. It’s very simple (reference "lower air deflector removal" photo). Right in the center of the tip of the nose of the car there’s a square recession. In that recession (if you look up into it), is a plastic pop fastener that almost looks like it should glow in the dark (it’s whitish green). You don’t loosen this. You push the lower air deflector forward (away from the vehicle) and it’ll come off that ledge and start to fall on you. It doesn’t weigh much, so don’t worry.

9. Once you have it off that ledge, start at the wheel wells and kind of pull it off on both sides, then push it toward the vehicle from the front and it’ll fall right off.

10. The next step is removing the bulbs from the front bumper. Note: there’s absolutely no reason to remove your grills, turn signal light housings, or foglight housings. Don’t waste your time or potentially break the plastic tabs off! From underneath the car, you can twist the bulbs for the foglights and turn signals out of their light housings. (Reference "foglight light bulb removal" image if you need to). You simply turn them about a 45 degree counter-clockwise turn and pull them straight out. (Note: if you’re like me, you’re going to replace these bulbs before putting your car back together. Mine are from 2006 and I’ve never had to change them before, so it's a great time to finally change them.)

11. Stop and look at the front bumper removal image so you're aware of what's coming up. (Reference "front bumper removal")

12. Now we’ll remove the bumper. There's an order you’re supposed to remove the bolts that hold the front bumper on. I'd say the order of steps 1 and 4 are very important, and not the typical order a person would do the task. The first bolt is a 10mm one in the wheel well. Use a ratchet. The second ones are the 5 plastic pop fasteners by the hood latch (above the Pontiac nose emblem), which are easily removed with the plastic prying tool. Third are bolts on the bottom (but they are already gone because we removed the lower air deflector already). Four are the last two bolts and they are really close to the outer edges of the headlights. The one on the passenger side is harder to remove because the windshield washer fluid tank gets in the way of a ratchet if you only own deep sockets like me. I used an articulated socket on my ratchet so I could use it at an odd angle. I then used a 10mm socket driver to fully remove the screw. Remove the passenger side one first since it'll be more difficult. Get a helper if you're nervous. The bumper pulls straight out. You can either have a friend or spouse help you hold one side, or you can stand in the center and pull it straight out and toward yourself and carry it carefully. You’ll need to unthread the wiring looms for the foglights from the styrafoam on the back of the bumper before you can walk away with the bumper. It’s really simple to detach them; unwind the wires from the styrafoam. Keep in mind that the polyurethane plastic bumper is more flexible than the paint. You don’t want to flex it too much. Be gentle when carrying the bumper. Instead of setting it on the concrete, you can throw some disassembled cardboard boxes or rugs under it. Or just go set it in the grass.

13. You can remove the 2 small plastic pop fasteners holding the plastic panel around the hood latch. That piece didn’t get in the way particularly, but it’s so easy to remove that you might as well do it just in case you need to put your light up there to see what you're working on later.

You now have a really good opportunity to wash these parts if you feel like it. You’re probably covered with random black soot by now and road debris. Wash these parts now and you won’t be as dirty when you put it all back together tomorrow. If you decide to wash everything, put masking tape over the holes for the turn signals and foglights so you don’t get water in their housings. I had to use a hair dryer to get the water out. Don’t hose off your car… just the pieces you’ve removed. I used car washing soap, a bucket, a rag, and a garden hose.

Also, note, for our cars, DO NOT mess with the fins on the radiator or condenser too much. The recommended way of cleaning them is with compressed air. You can use a shop vac to vacuum them off instead if you want. I had grasshopper parts stuck in mine...

2004-2008 Pontiac Grand Prix and GXP jacking instructions

jacking instructions

2004-2008 Pontiac Grand Prix and GXP front fender liner removal

front fender liner removal

2004-2008 Pontiac Grand Prix and GXP removal of retainers from lower front bumper

removal of retainers from lower front bumper

2004-2008 Pontiac Grand Prix and GXP lower air deflector (rock guard) removal

lower air deflector removal

2004-2008 Pontiac Grand Prix and GXP front foglight light bulb removal

foglight light bulb removal
(just twist the bulb out counter-clockwise...)

2004-2008 Pontiac Grand Prix and GXP front bumper removal

front bumper removal
(make sure to remove #4 last)

Photos to help with disassembly

These are in chronological order, from left to right, top to bottom. These images correspond with the process above.

the best location for jackstands to be placed

headlight removal

the tab to release the headlamps connector

the correct order if you're on the passenger side looking at the inner fender

the plastic bolt that prevents the deflector from falling off

what it looks like when the deflector is pushed off of this bolt

the lower deflector is ready to come off

twist the bulbs this far counter-clockwise and pull them straight out

don't remove these; the styrafoam is supposed to be connected to the front bumper

I only own deep metric sockets, so I had to use a universal joint socket to remove the bolt by the windshield washer fluid

socket drivers are great for the last few turns of loosened screws in tight areas

there's no particular reason you need to remove the crash bar. You'd need to get the bolts on that torqued properly anyway, so don't remove it. Disassembly is complete for now.

every hand tool I used for disassembly

if you wash the body pieces, put tape over the back side of the lights to prevent water from getting inside

vacuum or use compressed air on the radiator and condenser and wipe the crash bar so you stop getting filthy from it

Tools and parts for mounting the transmission cooler

Prices are from May 2021.

Online:

  • Tru-Cool Max Transmission Cooler 40,000 GVW 40k LPD47391 (in short, Tru Cool 40k) from Oregon Performance Transmission for $149.99 (they will automatically repackage the hoses and fittings so they don’t damage your cooler in shipping… which is AWESOME). You can buy the LPD47391 from Amazon if you prefer. You’re VERY unlikely to find anything remotely similar at the three big auto parts stores, so just plan on ordering it online. Note: this kit comes with enough rubber hose to plumb the cooler if you do it like my dad and I did it. We only had 6 inches left over. You won’t find the same size hose at O’Reilly Auto Parts. The size of the hose that comes with the Tru-Cool 40k is 23/64” (0.359) which is smaller than 3/8" (0.375). You'll have a very hard time getting anything smaller over the flare on the OEM transmission cooler lines, so keep that in mind. If you need more hose, you'll probably have to go with 3/8" because I don't know where you can get more 23/64". Anyway... this transmission cooler also comes with some mounting hardware, and we did use some of it, but we bought more hardware at Home Depot.

Home Depot: (I'll provide Amazon links as well if you prefer to buy online, but you're better off buying these parts from Home Depot because Amazon doesn't have everything. If you want to buy from Amazon, this 1/4" 20 TPI set appears to have most of what you need... but also, the Tru-Cool comes with a lot of lower grade screws to fill in what isn't in that set on Amazon)

where you'll find the Everbilt 3/4 in. x 48 in. Aluminum Flat Bar with 1/8 in. thickness

where you'll find every single screw, lock washer, nylon spacer, and hex nut I mentioned above

Parts you’re probably going to want to buy at the same time

Annoyingly, I had to visit several stores to get what I needed. Keep in mind that I could have potentially gotten everything from NAPA, but I simply don’t know, because I didn’t go there first. I went to O’Reilly’s first, Autozone second, and NAPA third. Prices are from May 2021. The goal was to replace the foglights and turn signal bulbs while the bumper was removed as well as replace fasteners that got broken during the transmission cooler mounting process. You'll break these in the process too, so you better pick some up.

O’Reilly Auto Parts:

  • DOR 963-026D – Dorman Retainer Assortment for $3.99. You’ll need the two black flat ones in this set, because you’ll destroy the two on the upper air deflector during the process described later. (AutoZone and NAPA might have these or similar)

AutoZone:

NAPA Auto Parts:

  • Two GXP turn signal bulbs 5702AK $4.49 each. The owner’s manual refers to these as 5702 KA. (AutoZone and O’Reilly definitely did not have these, and NAPA had them in the back warehouse, not on the bulb aisle, so an employee had to go look for them). If you have a regular Grand Prix, you’ll have no trouble finding your turn signal bulbs at O’Reilly or AutoZone. These stores definitely had 3757A (the owner’s manual specifically calls them 3757 KA) and plenty of them. Note: The bulbs for a Grand Prix should not be used on a GXP. You're going to need some luck finding these bulbs and I have no idea why.

the Dorman retainer assortment package... you only need these 2

the package for the foglights

Steps for mounting the transmission cooler

Keep in mind… the location we mounted this was NOT without compromises. This cooler is very large and all solutions will involve compromises. I had to modify the plastic lower air deflector (rock guard) because of how low we mounted this. If you mount it significantly higher, you’ll have to modify the upper air deflector and possibly other things instead. Had I known I’d have to have hoses hanging beneath the car, we would have investigated if we could have mounted the cooler higher, but it would have involved a lot more fabrication if we had. Note: It’s not a good idea to cut or notch metal pieces of the car, because if GM could have saved some money and weight, they would have. Your hood latch may not latch properly over time or some other issue might develop if you cut, notch, or remove any of the structural metal from the chassis. Modify plastic when possible because it isn't structural. We chose the location we did because it provided a great place to support the weight of the cooler and (as an added bonus) it hid half of the cooler behind the crash bar, which (I assume) has reduced its cooling ability a bit (people have said that they haven’t seen temperatures higher than 150 degrees with this cooler, so pushing that a little higher is NOT a bad thing. 170 or 180 degrees is a really good operating temperature for a transmission. You want the fluid to get hot every so often.)

1. Wait for your transmission cooler to arrive at your house. Go to Home Depot and the auto parts stores to get the supplies you’ll need. You don’t absolutely have to replace the bulbs, but I think it would be foolish to go through all this work and leave 15 year old bulbs in the sockets since they are so difficult to change with the bumper attached to the car. Note: some people (including myself) might be concerned about mounting a big silver radiator-lookin’ thing behind their bumper. Will it look awful? Should I paint it black first? Well, keep in mind that your A/C condenser and radiator are silver and they never bothered you before, right? The cooler will be nearly invisible, so don’t paint it. It also won’t work very well if it’s painted. You won't be able to see it unless you're looking for it really hard.

2. Remove your transmission cooler from the box and use masking tape to hold the LVP floor sample to the center of it. You’ll want this on there for two reasons. One, it’s going to create the empty space we desire for the cooler to have when it is mounted—you don’t want it resting on some other piece of metal. Two, it’s going to protect the fins a little bit while you’re test fitting it. You can also measure and mark the center of the bottom of the cooler if you want to with a Sharpie.

3. To make your life easier, remove the upper air deflector from the car right now. It’s a black plastic piece held on by the off-white pop fastener that held the lower air deflector from falling on your face. (Reference the "upper air deflector removal" photo). That off-white pop fastener removes just like the black ones you removed earlier. The upper air deflector also has two sacrificial black plastic fasteners in the upper radiator area you’ll need to remove. You can’t really reuse these fasteners because they will get damaged when you pry them out, so hopefully you bought the Dorman ones from O’Reillys I mentioned earlier. Use your plastic prying tools to remove these sacrificial black fasteners. You'll need to remove the ambient temperature sensor next, which easily pops out. (Reference the "ambient air temperature sensor removal").

4. We didn’t do this until later, but you get to learn from our process. Go ahead and mark the piece of flat aluminum bar you purchased at Home Depot to just cover the distance of the top mounting brackets on the transmission cooler. Saw off the excess and file it a bit smooth so you don’t cut yourself later. Mark the drilling locations on that bar and go ahead and drill them. Don’t attach it yet. I think it was 30.75 inches long once cut. You’ll end up using the screws and nuts that came with the Tru-Cool cooler, but you might want to hold off on doing that for now.

5. Put masking tape on your lower radiator core support. It’s hard to get a pen or Sharpie to stick to painted metal. You’ll be marking the holes you’ll need to drill in your radiator support based on the location of the brackets. We found the cooler to be best mounted slightly off-center. I can’t recall off the top of my head why it wouldn’t have mounted well centered, but it was a lot better for some reason being mounted perhaps 1 to 2 inches toward the driver’s side. If you decide to use a level, make sure your car is level first and/or make the cooler equally unlevel to match how unlevel your car is jacked up in the air.

6. Drill your holes. It’s easier (and more precise) if you start out with your 2nd smallest bit to poke/dent the metal and then make the hole, pick a midrange size bit and make the hole bigger, and then use your 1/4 inch bit to finish the hole off.

7. Test fit that your holes are in the right places (they better be!). Take your 2 inch Grade 8 hex cap screws and all of the Nylon spacers and see if it mocks up properly.

8. If everything is good, you need to take the cooler down now. Take those Grade 8 hex cap screws and work them into the lower radiator support from the inside to the out of the holes you drilled. It was difficult to do this, but it was worth it. We put a piece of masking tape on the screws and used pliers to guide the screws through the holes. I pushed upward on the radiator while my dad threaded the screws through the holes to create a little more room for the screws to be pushed from the inside.

9. Once that is completed, put your 1 inch and 1/4 inch spacers on. Put the transmission cooler back into position. Put on your Grade 8 locking washers and Grade 8 hex nuts. They only need to be finger tight right now. The direction of the lock washers does not matter.

10. The best way to mount the top of the cooler is by using the piece of flat aluminum bar I mentioned you should cut and drill earlier. Screw this onto the cooler’s mounting brackets. You’ll be mounting to the center support piece. Try to figure out where you’ll need to drill the center support piece (make sure you won’t be damaging that electrical connector that is very close to where you’ll be drilling). You’ll need to put the upper air deflector back in here 1 or 2 times to make sure it still fits. Note: if you are mounting the cooler identically to the way we did it, you won’t have to modify this upper air deflector, which was a surprise for us. If you are mounting it higher than we did… there’s no way you’re going to get this thing to fit back where it goes unless you modify it somehow.

11. We utilized one of the steel pieces of mounting hardware the Tru-Cool cooler came with. We bent it 90 degrees directly on the center of the 5th hole in it and cut it just after the 6th hole. We bent it with two pairs of Vice Grips. Do what you have to do to get a good 90 degree bend.

12. We drilled 2 holes in the aluminum bar and mounted the 90 degree L-bracket we made to it using 2 hex cap screws and hex nuts from the Tru-Cool hardware. We used one of the shorter Grade 8 hex cap screws, a Grade 8 lock washer, and Grade 8 hex nut for mounting to the center support piece. If we had enough hardware to use all Grade 8 stuff, we would have, but we didn’t know we’d need so many and didn't buy enough extras.

13. You can now remove your LVP floor sample and check and make sure you still have a good gap. Make sure your upper air deflector still fits. Tighten everything up, but don’t reinstall the upper air deflector yet, just in case it gets in your way. It’ll be very easy to put on later.

14. Unless you need to put the car back together (because you need to drive it before finishing the job)... Install the barbed fittings that came with the Tru-Cool kit to the cooler. We used Vaseline on the outer threads to lubricate them before being fitted. Not sure if that’s recommended or not. Follow Tru-Cool’s instructions they provided in the box.

LVP sample taped to the cooler

2004-2008 Pontiac Grand Prix and GXP upper air deflector removal

upper air deflector removal

2004-2008 Pontiac Grand Prix and GXP ambient air temperature sensor removal

ambient air temperature sensor removal

mark where you need to drill your lower mounting holes

mock it up and make sure it will work (it better or you've really screwed up!)

what it should look like after you have worked the screws into the lower radiator support so the threads face you

what your 90 degree L-bracket should look like after you make it

what your mounting situation should look like using that aluminum bar, the L-bracket, and other hardware

the gap once you have removed the LVP sample. Take note that we didn't mount the cooler perfectly centered. I don't remember exactly why...

purely due to luck and test fitting... the cooler doesn't interfere with the upper air deflector at all

Barbed fittings installed. Don't install them yet if you might need to put the car back together and drive it before plumbing the cooler.
(You won't be able to get the lower air deflector on anymore without cutting holes in it.)

Additional tools for plumbing the transmission cooler

1. Dental picks. I ordered these from Amazon… you only really need one of them… one that is very close to a 90 degree angle and NOT needle sharp. Assuming this link works for a long time… I used the one that is 3rd from the left. If the link no longer works, just buy one that is fairly small and close to a 90 degree angle, ideally with a flat tip. The actual tool the service manual calls for is a small bent-tip screwdriver, so that's also an option. Based on how infrequent I'll ever need to use a tool like this again, I chose the dental picks because they take up less space.

2. Utility knife (a Stanley Sport Knife with Quick slide is freakin' amazing if you don't already have one)

3. Assorted metric wrenches

4. Hair dryer (optional, but very helpful)

5. DEXRON VI transmission fluid (I used Castrol which I purchased from AutoZone). You can buy it on Amazon if you want, Valvoline is good too

6. A funnel with a small tip that fits inside the transmission dipstick tube. (I own a Hopkins FloTool spill saver funnel).

7. Hose cutter or PVC pipe cutter, either one will work.

8. Update: 5/8 Inch rubber cushioned clamps. I haven't used these yet, but these will take the place of zipties for securing the rubber hoses to the car. I believe 5/8" is the correct size. I believe the OD of 3/8" ID hose is around .55", 5/8" (.625), or 11/16" (.6875) based on some Googling, so 5/8" should be about the right size to not pinch the hose. I'll update this page once I have installed them. You'll use some short self-tapping screws (like what you find on the HVAC equipment in your house's attic... which probably has a dozen extras of these scattered around the insulation) to attach them to the chassis of your car. If 5/8" clamps ends up not being tight enough, electrical tape can be used to make the hose bigger in diameter in that spot. Again, I'll update this site if the size is correct and with new photos once I've used them.

Steps for plumbing the transmission cooler

1. The OEM transmission cooler line going into the upper part of the radiator is easiest to remove first. On a GXP, it is on the driver’s side and very obvious at the top of the radiator. There’s a little plastic piece you twist off. Then you have to remove the Quick Connect Fitting (reference "Quick Connect Fitting removal" image). You use the dental pick to grab and rotate the retaining ring/clip. It's actually quite difficult, but it'll fly off eventually.

2. You don’t need to care about whether you lose the retaining ring, because you won’t be reusing it.

3. Position your drain pan underneath and pull the cooler line straight out of the fitting. If you haven’t driven your car very recently, you might only lose a few drops at this point. Note: You do not need to remove the actual fitting from the radiator at all! If you decide to... Do not remove the upper and lower transmission cooler fittings from the radiator at the same time otherwise the OEM transmission oil cooler will fall inside the radiator end tank. (Reference "transmission cooler lines" image if you want to see how these connect to the radiator. Note: this image is of the radiator in a V6 Grand Prix. In a GXP, the transmission cooler lines enter the radiator on the driver's side, not passenger side).

4. In order to do the lower one, you’ll need to turn your steering wheel all the way to the left or remove the wheel in order to get your head inside the wheel well where you can see what you're doing. Turning the steering wheel works just fine. Inside the driver’s side wheel well there is a plastic splash shield held on with 3 plastic pop fasteners with phillips head screws in them. (Reference "splash shield removal" image if necessary). Loosen those with a screwdriver. If they have difficulty coming out, use your plastic tool for removing these and push away on the plastic portion while you unscrew the screw or pry upward on the screw while you’re twisting it. These can be annoying and not come out very easily, but you’ll get the hang of it.

5. Set that panel aside. Get a flashlight. You should now be able to see the lower transmission cooler line on the radiator. Remove the quick connect retaining ring. Position your pan underneath. Pull the cooler line straight out. You should lose at least 1 cup (or more) of fluid and it will continue to drip for quite a while. (Note: like most people, we didn't plug the Quick Connect Fittings on the radiator, so every time I drove the car for a few days, a bit of transmission fluid would leak out of the OEM transmission oil cooler inside the radiator. This is no big deal. Put a flattened cardboard box under the front of your car in your garage and just let it leak out till it stops.)

6. Note: you may want to plumb the car differently from how my dad and I did it. The way we did it used the least amount of new parts, but did come with its own compromises. If you prefer to complicate your life (or if your existing transmission lines are corroded and unusable), I've provided a list of Possible Alternative Parts you might want to use further down this page).

7. You’ll now need to make sure the lower air deflector (rock guard) fits. It won’t fit if you mounted your cooler exactly like we did. You’ll need to make a notch for each of the 2 nylon pieces and make two 50-cent piece coin-size holes in the lower air deflector for the cooler's barbed fittings to go through. You can make these easily using a hair dryer to soften the plastic and a utility knife. The hairdryer makes the process easier, but is not required.

8. You’ll need to hang the lower air deflector from that glow-in-the-dark looking plastic bolt while you work on plumbing it so make sure things still fit.

9. Like I said above, you may want to come up with your own plan, but what we did worked after some effort. You can reuse the stock transmission cooler lines (like we did) and connect your hoses directly to those lines. Or… you could remove the lines and plumb directly to the transmission. Or… you could cut the rubber portion of the stock transmission lines and use additional double-sided barbed fittings (similar to a hose repair kit). Or… you could remove the crimp connections and reuse the barbed fittings underneath those supposedly with some screw clamps. There are a lot of options, so choose your own adventure. I only know how to do what we did. Originally, I was going to go the -6AN fitting route, but it seemed like more trouble than it was worth, and so I returned almost $200 in AN parts to Amazon that I had purchased in case I needed them. The parts and hose with the Tru-Cool kit were high quality enough in my opinion. I discussed these parts below in a section called Possible Alternative Parts.

10. If you’re doing it like us, you’ll need to remove the piece of metal holding the two transmission lines together (reference "transmission cooler lines" image). Then adjust the upper transmission cooler line to be underneath the car by gently moving it. It can be positioned near the driver’s side tire area without much trouble. Move the lower line to be closer to the center of the car.

11. Get your 23/64 hose from the Tru-Cool kit. It should be plenty for the install if you’re copying us. You’ll actually have 6 inches leftover if you copy us. (Note: unless you are plumbing an inline cooler or a bypass, it doesn't matter which hose goes where if you're plumbing your cooler in a standalone configuration. In other words... you don't need to know the direction of the flow.) Thread the screw clamps onto the hose. This hose will be very tight, so it works great. Because it is so tight, it will be helpful to lubricate the inside of it with some of the transmission fluid from the pan and heat the end of the hose with your hair dryer for a dozen seconds or more. It’ll be less of a struggle to get it on the flares of the cooler lines you pulled out of the radiator earlier if you lubricate and heat the hose up a bit. It's still going to take a lot of strength, so get ready to grunt and sweat. Use a single screw clamp on each connection. Tight, but not so tight that it digs into the hose.

12. If you are copying us, you’ll thread the passenger side hose through one of the existing holes in the lower air deflector.

13. Reattach that metal piece that was holding the cooler lines together to the radiator/fan shroud if you can/want to. My dad said he reused it, but I don't think so. I haven't removed the lower air deflector and checked, but I'm pretty sure that piece is sitting in my toolbox....

14. Attach the lower air deflector to the car.

15. Ziptie the driver’s side hose to the lower air deflector to give it some support. Make sure you don't bend a hose too much. You need gentle arcs. If you bend a hose too much, it could kink, and goodbye transmission.

16. I added 10 oz of transmission fluid. It’s difficult to know exactly how much to add, so try to guess based on how much you lost, plus add a little more than that since you’re now having to fill a few extra feet of hose. I was at 21,000 miles since my last transmission fluid and filter change, so I didn’t care too much about being at the exact proper level. I was scheduled to get my fluid and filter changed in two days anyway.

17. Temporarily ziptie the foglights together and rest them on top of the lower air deflector to prevent them from falling and getting damaged while you drive. Test drive the car if you can safely do so in your neighborhood before putting it completely back together. Keep in mind that if you’re driving through standing water or puddles, it’s going to get into places it shouldn’t because your inner fender liners are removed.

18. If you’re like me, you’ll hear some gurgling as it gets rid of air. Take it easy. If your car is slamming into gears, use your best judgment. Mine was driving flawlessly. I drove around the neighborhood for multiple laps and it got up to 140 degrees. Make sure to sit in reverse a while, neutral, park, drive, and manual mode. You want to test everything. (You don’t need to drive in reverse, just sit there with your foot on the brake for around 30 seconds while in gear. You could drive a few feet in reverse if you want, but nothing crazy).

19. Take it home and visually inspect whether your connections are leaking while the car is running. We didn't have any leaks. Check the fluid level while the car is running. I was a little low and added (I think) the rest of the quart, or just around 6 or 8 oz. Put your car back on jackstands and go take a break while the engine cools off for a while.

20. Replace your light bulbs while your hands are clean. Put the splash shield back on in the wheel well next. Put the car back together in the opposite order of how you took it apart. It should go back together even easier than it came apart. These screws all technically have torque values, but they are all pretty easy to figure out manually. None of them take very much torque at all. You’ll need someone to hold the other side of the front bumper while you reattach the other side, or you could stack up cardboard boxes to hold it up for you while you slide it in.

21. After putting the car back together, we used some zipties to add some support for the driver's side hose. Like I mentioned above, I have purchased some 5/8 Inch rubber cushioned clamps. I'll update this site if the size is correct and with new photos once I've used them.

2004-2008 Pontiac Grand Prix and GXP Quick Connect Fitting removal

Quick Connect Fitting removal

the upper line won't leak much if you haven't driven in a day or so

2004-2008 Pontiac Grand Prix and GXP transmission cooler lines diagram

transmission cooler lines
(note: on a GXP, the lines enter the radiator on the driver's side, not passenger side like the image above (which is for a V6 Grand Prix))

2004-2008 Pontiac Grand Prix and GXP splash shield removal

splash shield removal

with the splash shield removed, you'll be able to see what you're doing

lower transmission cooler line on the radiator

once you pull the lower line out, you'll lose at least a cup of fluid

pull and adjust the lines after removing the piece holding them to the radiator fan shroud

this is where we had the OEM transmission oil cooler lines adjusted to when we started plumbing them. The upper on is on the right, and the lower is toward the center of the car

click this image to see the 4 places I had to cut the lower air deflector

plumbing complete. Fill with some new DEXRON VI fluid from the dipstick tube.

make sure to ziptie your foglights together so they don't fall off the lower air deflector while test driving

make sure to use your new Dorman fasteners when putting the upper air deflector on the final time

if you didn't have any leaks on your test drive, let the car cool off and then put it back together

we used a few zipties to help support the driver's side hose since it's kind of just floating there

another view of the ziptie situation. You can actually screw clamps into metal parts of the car's body, but we didn't have any for holding hoses. I purchased these, and determined 5/8" was the correct size, but I haven't installed them yet. I wanted to see if the solution below helped enough or not.

all done!

the cooler is nearly invisible

it's hard to believe this is after driving the car 35 minutes

Due to noise/vibration sounds when the transmission fluid temp is lower than 130 degrees, we made some modifications to the way the transmission oil cooler lines were left and redid the zipties with better quality zipties.

There's still a bit of noise that is only noticeable at a complete stop in Manual mode in 1st gear (it goes away if shifted into Drive or 2nd in Manual mode) when below 130 degrees, but using zip ties to hold old pieces of hose around these pieces decreased the volume of noise a bit. I assume I have a hose that is at a strange curve or something, and I'll have to check it someday.

I'm finished. What are my results?

The highest transmission fluid temperature I have seen so far has been 167 degrees one day when it was 86 degrees outside and I had a 30 mile drive in rush hour traffic with 4 highway changes. So far this summer, the weather has mostly been in the 90s, and the transmission fluid temperature seems to mostly stop increasing at around 158 degrees.

Overall, I absolutely love it. It's transformed my car from something I had to make excuses for* to a car I can actually drive like any other car. An added benefit (though, not to my wallet at the gas station), is that it permits me to drive more aggressively now that I don't have to worry about heat harming my transmission with excessive heat. So far my average mpg has dropped from 14.8 to 13.4 mpg but I'm also running the A/C harder because it's the middle of Summer now, so that's an impact too.

*= I've been paranoid the entire time I've owned my GXP (since Jan 2009). I've watched the transmission fluid temp reading on the DIC, and would start to worry when it got close to (or above) 200. Therefore, I'd only drive my GXP on short drives, typically drives less than 30 minutes. I'd avoid going optional places (roadtrips) in the car, because I didn't want to risk damaging my transmission.

Other pros and cons?

Besides the ones I mentioned above...

  • The engine temperature gauge seems like it is lower during most of my drives than it normally would be with the inline transmission cooler lines through the radiator being used.

  • I have to be more aware of how far I pull forward when parking. The hoses hang down a little more than the plastic on the air dam and are within millimeters of it. I don't want a curb to scrape or tug on the hoses. There's steel inside the hoses, but still. It's even more important to leave my car's rear end hang out of parking spots a bit more.

  • Manual mode (how I have always exclusively driven my GXP) is noisier at a complete stop in 1st gear when the transmission fluid temperature is below 130 degrees for some reason. It's particularly noticeable around 122 degrees, but is audible starting around 117 degrees. At 130 degrees, the excess noise goes away. Shifting into 2nd gear (or changing to "D") at the same complete stop gets rid of the excessive noise no matter what the fluid temp is. (Note: that does mean I have to take off from the stoplight in 2nd gear, as an immediate shift to 1st and then hitting the gas is an abrupt and hard transition for the transmission and should be avoided.) I might have some vibration resonating due to (perhaps) hoses vibrating on something. It's hard to identify since it is only possible to witness between ~117 and ~132 degrees while in manual mode, in first gear, with my foot on the brake, and it's not loud enough for a video recording to capture the sound. The sound goes away the moment I shift into Drive or into 2nd gear (while still in manual mode) at the same complete stop. I'll track it down eventually... Since this issue wasn't present before the transmission cooler was installed, my assumption is that the fluid is running at a high pressure when in 1st gear at a stop, and when the fluid is cool, the low RPM of just idling at a stoplight or stop sign causes the fluid to not flow as easily. This is likely due to the fact I completely reused the OEM transmission oil cooler lines and relocated them by taking advantage of them having a flexible rubber hose component, and just pulling and pushing them into a new position. I don't think I have a kink in a hose, but I do believe I have either a slightly restrictive bend or a major uphill area in one or both of them, causing the fluid to not flow as easily at low RPM in 1st gear at a complete stop. Worth repeating: this noise is not present until approximately 117 degrees and it goes away at around 128 to 132.

  • The transmission fluid takes a long time to heat up, which is good but also requires me to baby the car a bit until it gets ~120+ (just as you would/should even if driving the car without an external transmission cooler). On my 8 mile (25 minute) drive to work, I can generally expect to see 140 degrees. I often wonder if I could have gotten away with using the Tru-Cool 30K, or if it would be incapable of cooling the fluid enough when it's 100+ degrees outside. It would have been easier to install due to its smaller size and because of its barbed hose fittings being on the side instead of bottom. Update: a year after my installation, I still wonder if I could have gotten away with the TruCool 30k... it would have been a lot easier to install.

  • In the winter, as I suspected, I can make it all the way to work before the transmission reaches 130 degrees. Besides the annoyance of having to shift to D or 2nd at stop lights to avoid hearing the annoying noise I mentioned above, I did not see or experience any problems. I have read about people putting cardboard or coroplast over their coolers to make them less efficient during winter, but (1) I don't fully understand how they are attaching it without going through a lot of trouble, (2) I don't want to go through a lot of effort to do it, and (3) I don't want to create a rattle or other noise. The combustion temperature of cardboard is 800 degrees Fahrenheit, so I don't think it's a fire hazard, however, I don't like the idea of using cardboard because of rain, snow, and washing my car causing the cardboard to disintegrate. Coroplast combusts at around 600 degrees Fahrenheit, so I think it's a better idea since it won't care about getting wet. However, I personally believe the TruCool 40k is a bit overkill for these cars. A smaller cooler like the 30k probably would have worked just fine, so I wish I had tried one of them first.

  • I've read about people using coolers with electric fans on them (and suggesting them to others). I am only mentioning this because I think the idea is absolutely ridiculous. I think this would be a complete waste of time and money for a GXP. We have a great location for mounting a giant cooler, and the Tru-Cool 40k performs so well, that I have not yet seen "operating" temperature (170 to 180 degrees). I have not had to sit in a huge traffic jam yet, but all of my driving is stop and go. I don't think GXPs need a fan and I think adding one to a TruCool 40k would actually be cooling the fluid too much and thus harmful. I haven't noticed a negative impact to my air conditioning or engine temperature by having a TruCool 40k mounted in front of them and I see absolutely no reason for anyone to run an additional fan on a TruCool 40k on their GP GXP.

Update from Summer 2022

It has been a very hot summer this year (unlike last year) with multiple days in a row in the 100s. I heard what I assumed to be some worrisome noises in 1st, 2nd, and 3rd on a day that was 109 degrees when I was driving home for 45 minutes. I took the "rock guard" off and started looking around. I didn't really find any problems, but while down there, I used a Dremel and enlarged the holes and cut off pieces of plastic that might be squishing the transmission cooler hoses and/or making things not fit back together well. You'll notice that I hit a new record for hottest temperature this day... 176 degrees.

The TruCool 40k is certainly more than enough to keep my GXP cool. I often tell people that they should try the TruCool 30k instead, just because it seems like the 40k is more cooling than necessary, and the installation of a 30k would be much easier. For my driving conditions, the 40k provides too much cooling. I would not have been offended if on a 109 degree day my 45 minute drive caused my temps to be 190-200. I don't know if the TruCool 30k would perform that well, but I sure do wish I tried, since I had such a hard time fitting the 40k thanks to (1) its size and (2) the nozzles being located on the bottom instead of the side.

Not very many of the photos I took during my ~9 hour process last weekend are all that worthwhile to share. I'll include some below, but here are some new tips:

  1. Enlarge the holes that you cut in the "rock guard". The one where I used a factory hole was actually causing the rubber hose to slightly kink. Enlarge them bigger than they need to be, so you don't have a super hard time getting the rock guard on and off over the clamps on the transmission cooler itself. You need to be able to take it off without removing the hoses, and that was difficult for me to do.

  2. Cover the metal transmission cooler lines (if you decide to reuse the OEM ones) with excess rubber transmission cooler hose and ziptie it around them. That way if something is going to potentially rub, it'll rub on the hose instead of the metal. Just cut the excess hose about the right length, cut it down the middle (hotdog bun style) and ziptie it around the metal cooling lines.

  3. I hate plumbing, but if you are more experienced and skilled than me, don't reuse as much of the OEM lines as I did and you'll probably make your life a little easier. I just didn't want to have to work harder, and I probably should have.

  4. I'm not sure how important this is, but I didn't like it when I discovered it. Try to make sure one of the OEM cooler lines is still in the holder to prevent it from moving. Mine were very loose and it wasn't causing a problem, but according to the illustrations from the shop manual, one of those 2 cooler lines is supposed to be secured to that plastic thing. (See photo below).

  5. I also had a leftover metal bracket part last year, and I put it on these two lines so the secured one would prevent the other one from moving as well. I don't know if this piece was originally near where I put it... but it sure did fit perfectly. (Again, see that same photo below).

  6. Cut the rock guard to not interfere with the way your transmission cooler is mounted as well as where the hoses are running. I didn't modify mine enough and it was hell to get the rock guard off and back on again this time (by myself). (I included a couple photos of what areas I cut off this time, but I also cut another one toward the front that was causing me hell to get the rock guard on past the center bottom bracket behind the cooler.

Highest temp I've ever seen with 40k.

Enlarge this hole to make your life easier.

Enlarge that top hole and round it into an oval shape to make your hose less likely to get a small kink in it. Mine wasn't kinked, but it was certainly getting pressed on.

Left is how I had it. Middle shows one line clipped into the factory plastic clip (that has 2 spots... but I swear both will not fit. I bet it's a piece reused from a regular GP, where perhaps both lines are closer to one another) and the metal bracket clip we didn't reuse last year--it snapped right on. Right pic shows another view of the factory plastic clip and a little piece of rubber hose I added to pad the two metal lines.

Be braver and cut more of the material off so it doesn't squish hoses or interfere so much.

I took a very large amount of plastic out of this area so one hose could be routed through this area without getting squished. I also covered the metal line with rubber hose so I could connect zip ties together to suspend this hose from the bottom bracket of the transmission cooler (see white zip ties for that... they may be hard to see in the photo).

Other Helpful Documents

These are other pages from the Service Manual that might help you on related tasks if your install isn't as straight forward as mine... particularly if you need to remove the OEM lines from the transmission and do more work than me.

2004-2008 Pontiac Grand Prix and GXP fastener tightening specification

fastener tighting specifications

2004-2008 Pontiac Grand Prix and GXP installing quick connect fittings 1

installing Quick Connect Fitting-1

2004-2008 Pontiac Grand Prix and GXP installing quick connect fittings 2

installing Quick Connect Fitting-2

2004-2008 Pontiac Grand Prix and GXP installing quick connect fittings 3

installing Quick Connect Fitting-3

2004-2008 Pontiac Grand Prix and GXP transmission cooler hose replacement-1

transmission cooler hose replacement-1

2004-2008 Pontiac Grand Prix and GXP transmission cooler hose replacement-2

transmission cooler hose replacement-2

2004-2008 Pontiac Grand Prix and GXP transmission cooler Quick Connect Fitting connector replacement

transmission cooler Quick Connect Fitting connector replacement

2004-2008 Pontiac Grand Prix and GXP transmission cooler removing transmission cooler lines from transmission

removing transmission cooler lines from transmission


2004-2008 Pontiac Grand Prix and GXP transmission cooler installing transmission cooler lines to transmission

installing transmission cooler lines to transmission

2004-2008 Pontiac Grand Prix and GXP transmission cooler Page 1 of TSB Bulletin No 04-07-30-017B (a notice about how transmission line fittings were changed in 2004)

Page 1 of TSB Bulletin No 04-07-30-017B (a notice about how transmission line fittings were changed in 2004 (as well as their torque specs))

2004-2008 Pontiac Grand Prix and GXP transmission cooler Page 2 of TSB Bulletin No 04-07-30-017B (a notice about how transmission line fittings were changed in 2004)

Page 2 of TSB Bulletin No 04-07-30-017B (a notice about how transmission line fittings were changed in 2004 (as well as their torque specs))


Possible Alternative Parts

When I was preparing for this "operation" I ordered every part I could find (via my research) that I might need for the job. This involved reading forums and Facebook posts, some of which were very difficult to understand. I've attempted to identify exactly what you'll need for these alternative installation tasks, but I didn't actually end up using any of these parts, so you may need to do more research.

If you want to go the -6AN way...

There's two ways you could utilize these. You could simply use them on the Tru-Cool 40k with some 6AN adapters (see below) and then utilize 6AN fittings on the transmission cooler. You could still connect to the OEM transmission oil cooler lines with screw clamps unless you used braided steel hoses. Or... if you have no intention of using the OEM transmission lines at all, you could plumb directly from the transmission to the cooler in a standalone configuration. This would be a good idea if your lines are corroded and unusable.

Various other parts you might find handy...


Donations

Reference/Credit

A large portion of the diagrams on this site are from me reconfiguring information from an online service manual since my digital one I own is missing the transmission section for some stupid reason. That site is a great resource, but terribly difficult to navigate, so I'm providing several reference links below. About half of these are procedures I didn't decide to cover on this site.

Here is the procedure for checking the transmission fluid

Filter and seal replacement

The notice about how transmission line fittings after 2004 were changed

Trans cooler hose replacement

Quick-Connect Fitting Replacement

Transmission Fluid Cooler Hose/Pipe Connector Replacement

Fluid Pan: Specifications

Transmission fluid pan removal procedure

Transmission Cooler: Service and Repair

Front Fender Liner Replacement