Engine Cooling
Also see Cooling system airflow
General engine coolant flow:
Coolant is a mixture of antifreeze and water.
It starts in the radiator, flows from the lower radiator hose to the water pump.
Coolant is pumped through the water pump and out of the two outlets at the rear of the water pump, splitting the flow to each side of the engine block.
Coolant comes out of the block at the top around each cylinder. Small holes in the head gasket restrict the coolant to create an even flow front to back, side to side around the cylinders
Coolant flows through the cylinder heads, back to the front of each at the intake manifold. The coolant merges back together and then through the thermostat.
The thermostat controls the minimum normal operating temperature of the engine. When hot enough, the thermostat opens(some close a bypass as well) and sends the hot coolant through the upper radiator hose to cool the coolant. The coolant moves through the radiator towards the opposite side, where it collects and is returned to the water pump, starting the entire process again.
Heated coolant for the heater(s) comes from the top of the intake manifold(front or rear) and moves through the heater core(s) then back to the water pump inlet or radiator tank. This could be a port on the water pump, a fitting in the lower radiator hose, or a port on the radiator itself.
The radiator cap allows a specified amount of pressure to build up in the entire cooling system, which raises the boiling point of the water/coolant mix preventing overheating.
Overheating:
The combustion inside the cylinders and friction of moving parts inside of our engines generates a LOT of heat. Air, oil, and coolant help remove heat from the hottest parts of our engines.
The water pump moves the coolant through the engine where the heat is transferred from the block to the coolant. The coolant heats up causing the thermostat to open, setting the minimum normal operating temperature of the engine. The open thermostat allows the coolant to flow to the radiator and also to the heater core(s) which are mini radiators. The radiator fan or vehicle speed forces air through the radiator, allowing the heat from the coolant to transfer to the air, keeping the engine cool.
Things can go wrong at any step of this process, and while the dash temperature gauge isn't super accurate it is usually the first indicator that something is wrong. It's normal for an engine to get slightly warmer with one or more of the following: heavy loads, going up steep grades, higher altitudes.
Causes of overheating:
Low coolant level - obviously the coolant can't do it's job if there isn't enough - check/fill
Faulty radiator cap - leaks or doesn't allow normal pressurization of the system - pressure test the cap and the system
Leaks(gaskets/radiator/pipes/tubes/hoses) - allow depressurization and air into the system - identify/fix leaks and pressure test the system
Air bubbles in the system - heat transfers to the liquid coolant a whole lot faster than it can transfer to air - ensure that the system is air tight, pressurized and all bubbles have been worked out of the system, pressure test the system
Thermostat stuck - if it's stuck closed the engine can overheat, if it's stuck open the engine will never make it to proper operating temperature(causes other problems) - test/replace thermostat
Fan clutch - when your fan clutch fails you usually notice it at slower speeds - you can test the fan clutch with an RPM gauge
Water pump - they can leak and the shaft/propeller can break/corrode - replace the pump, pressure test the system.
Drive belts - broken/slipping drive belt affects the radiator fan and water pump. - check/replace
Antifreeze/water ratio - too much antifreeze in your coolant and it won't transfer heat as effectively, so make sure you ratio is correct. If the ratio is too low it can cause jelling or even freezing at really cold temperatures and a lower boiling point of the coolant - jelled coolant can't circulate - check and adjust antifreeze/water ratio.
Blocked radiator - most common blockage is from the front where it prevents the air from passing over/through the fins, however it can also get blocked internally and reduce the amount of coolant flow - clean the exterior, flush/replace coolant and/or radiator
Blocked AC condenser - the AC condenser sits in front of the radiator, so it can block the airflow when it's dirty/damaged
Radiator/Fan Shroud - if your shroud is missing or has been modified, it may not allow the fan to pull air across the entire radiator, decreasing it's effectiveness - repair/replace
Modified bumpers/grills - This can cause airflow issues to the radiator, esp large winch type bumpers. If your replacement bumper is higher or sticks out more than the original, it can cause airflow issues - modify/replace
How hot is too hot?
Well that depends on few factors, but generally speaking for our engines you really don't want sustained temperatures above ~230f. If you notice any steam coming from the engine area, or the temperature gauge is approaching the red zone, check gauges lights coming on, all are bad signs.
What about too cold?
Yes, believe it or not, too cold causes problems as well. Your engine may not get up to normal operating temperature due to a partially or fully stuck thermostat, or maybe someone installed the wrong temperature thermostat by mistake or on purpose. Here are some problems that it can cause.
The PCM stays in open loop mode
Poor fuel economy
Metal pistons and rings don't conform as well
Increased engine blowby
High emissions
Increased sludge, ~1 gallon of water per gallon of fuel burned
Coolant: Hint, color doesn't determine the type of coolant, each manufacturer chooses what dye to use, see chart below.
Virtually all of our automotive coolants are Ethylene Glycol based with different additive packages. What we think of as regular coolant is green in color, but that doesn't tell the whole story as each MFG can decide what color to make their coolant/antifreeze mixtures. Coolant ratio is extremely important, for both boiling and freezing points and you should never run straight water. At sea level atmospheric pressure, the boiling point of Ethylene glycol is 197.3 °C (387.1 °F), Propylene glycol is 188.2 °C (370.8 °F), water is 100 °C (212 °F) a mix of 50/50 Ethylene glycol and water has a boiling point of 106°C (222.8°F).
IAT: Inorganic Additive Technology, phosphate-silicate additive package what we think of as 'conventional coolant/antifreeze'. typically dyed green 2yr/30,000mile intervals used in 95 and earlier vans.
OAT: Organic Acid Technology, sebacate and 2-ethylhexanoic acid additives, Dexcool and other universal coolant/antifreeze, typically dyed yellow or orange but can be pink/red/purple/green as well, ~5yr/150,000mile intervals used in 96 and later vans. Up to 8% better heat transfer than IAT coolants.
HOAT: Hybrid Organic Acid Technology, like OAT but usually contain some silicate, up to ~10yr/180,000mile intervals depending on coolant.
Prestone Platinum says it's good for 15+yrs 350,000miles which will be my next go-to fill.
Can you mix coolants?
Short answer, yes the MFGs say that you can mix conventional with Universal/Dex/OAT but you would use the lowest service interval. If you are doing a complete drain/flush fill, use what GM recommends, IAT based for 93 and earlier, and OAT based for 94 and later.
Thermostats:
Thermostats determine the baseline temperature of the engine, the lowest normal operating temperature. These should normally be left at the stock temperature. If you go too low it affects emissions, moisture content in your oil, can even stop the torque converter clutch from locking up. The highest temperature that your engine sees is not determined by the thermostat, but many other factors such as load, fuel/air mixture, cooling system condition, airflow across radiator, etc.
Larger Radiators:
There are thicker core radiators available as drop-in replacements for Astro/Safari vans(check amazon/ebay). I used a 3-row all aluminum for my last upgrade. There are also universal fit radiators that you can buy, but then you have to fabricate your own mounts.
Electric Fans:
Electric fans were not available from the factory on any Astro/Safari vans. Many different electric fans can be used from the aftermarket or alternative application OEM fans. The 1gen body style and the 2gen body style use different sized radiators and so would require a different fan/shroud setup.
Electric Fan Control:
Our vans were never set up to control an electric fan, though some PCMs have an output that could be enabled depending on your ECM/PCM.
Hayden Automotive 3653 Economy Adjustable Thermostatic Fan Control(30amp)is a great and economical option for switching your fans on and off http://amzn.to/2pTjJE8
This one is probably the cheapest and easiest to install, however you may want to add a relay to do the heavy lifting. Relays are dirt cheap to replace, cheaper and easier than replacing the controller. http://amzn.to/2p8BceI
Simple control of electric fan(s) up to 30amp using thermoswitch and relay. Jegs 10560 http://amzn.to/2pSv8Gq Can also be made yourself using appropriate parts, can substitute an adjustable thermostat control like the Hayden above in place of the thermoswitch in the diagram below. https://photos.app.goo.gl/sZ8AoKd7rZh4FDUg2
Note: multiple types of thermoswitches are available, please ensure you get the right kind/temperature. If you are going to install in-line with a hose(not grounded) you should use the two prong type or use an adapter that has a grounding screw built in.
Here is an example of a thermostat housing that has threaded holes that can be used for a thermoswitch https://amzn.to/2ZJv2C1 or you could use an inline adapter with a built in grounding screw for a temperature switch/gauge: http://amzn.to/2zdlCiu
Piecing together the above can easily be done, and can be customized to your exact needs. 30/40amp relays http://amzn.to/2p8BceI 30amp self-resetting circuit breaker http://amzn.to/2pOwBx2
PCM Control(has to be enabled with a PCM tuning software/hardware)
https://www.astrosafari.com/viewtopic.php?f=43&t=126738&start=80#p1513430
http://www.littelfuse.com/data/en/application_notes/an9312.pdf
Electric Water pumps:
While not something that I would see being valuable for me, at least they exist for someone that is interested.
Davies Craig EWP150 ($230) or 8870 kit($450) with Controller(also controls electric fan)
http://www.gearhead-efi.com/Fuel-Injection/showthread.php?6149-1227747-electric-fan
1227747 electric fan control ------ I'm not sure if this information has been shared or not. I couldn't find it. The 1227747 ecm is not set up to control an electric fan. However, if you are not using an a lock up torque converter, you can use the ground signal from A7 to control the fan relay. See the attached picture for the TCC parameters I changed. Using the TCC - minimum CTC for TCC lock as the fan on temperature is the only parameter you have to experiment with. The only weird thing is the actual temperature that the fan turns on is about 20 degrees C higher than what is in the TCC - minimum CTC for TCC lock is set at. I'm not sure why.