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There are many forum articles discussing Chris Crafts with 427 Ford engines overheating, especially when running on plane. The general consensus seems to be that overheating can be caused by poor maintenance (raw water impeller shedding blades), but even with proper maintenance the cast iron OEM engine oil coolers corrode from the inside and are prone to blockages. After I replaced the impellers that were on the boat when we bought it, I was still seeing engine temps as high as 190°F even at low cruise speed (~1800-2000rpm). So I took the cooling system apart.
I sent the main heat exchangers off to be boiled out and resoldered where there was evidence of leaking. I also had the shop add a fitting for a pencil zinc.
With all of the hoses removed, I found the marine gear cooler fairly packed with bits and pieces of previous impeller blades. After removing them, I replaced all of the hoses and clamps with new ones. That seemed to improve the situation somewhat, but I was still seeing higher temperatures than I like, especially on the starboard engine. Since we rarely run on plane, I basically just tolerated the situation for several years.
Then, in 2020, the starboard engine got hot (195°F) one day despite the fact that we were barely above idle. I dug into the cooling system, and the following pictures show what I found.
The oil and gear coolers are under the right side exhaust log of the 427 Chris Craft/Ford engines. On the starboard engine, that means you have to crawl outboard of the engine for access, which is awful in any case.
The outboard access is pretty tight here.
The view from the top shows how incredibly tight access is to the gear cooler. And that's with the heat exchanger support that bolts to the gear mount removed.
This is looking at the side of the marine gear cooler. As you can see, access to this very important maintenance item is horrible. The gear mount blocks access to the rear, the gear blocks access to the far side, the engine and exhaust log block access forward, and the stringer blocks access to the near side. My guess is, the Chris Craft engineers were given the task of making these marine propulsion packages small, rather than also considering ease of maintenance.
This shot was taken from the underside of the engine and gear looking up into the gear oil cooler after I removed the raw water hose. As you can see, several of the holes that raw water is supposed to flow through are full of goo. That could certainly impede raw water flow, which would affect cooling.
I finally gave up trying to access the gear oil cooler without doing major surgery. Instead, I did minor surgery by draining the antifreeze and removing the hose to the heat exchanger. After loosening the clamps on the hose that connects the heat exchanger to the gear cooler, I was able to lift the HEX clear and finally see inside the gear cooler from the top.
Looking down inside the gear oil cooler, you can see that the top of the raw water tubes weren't blocked with goo like the bottom. I pushed a stiff pipe cleaner brush down each of the tubes to clear them, then reinstalled the heat exchanger.
With the heat exchanger reinstalled, I installed the hoses and used a garden hose to back flush the HEX, the gear oil cooler, and the engine oil cooler. I hadn't back flushed the system before, and a few small bits of old impeller blade came out of the engine oil cooler. Then I reinstalled the raw water pump and went for a drive.
Initially, the results were good. The starboard engine was no longer overheating and the temperatures were consistent on both sides. But then the problem returned again on a trip back from Mattawoman Creek. At first, everything was normal. We were cruising at 2,000rpm and the temp gauges read 160°F on both sides.
But then I started noticing the starboard side was creeping up. As it passed 180°, I reduced throttle on the starboard side, first to 1,500, then 1,000, but the temp on that side kept rising, passing the 190° mark, so I shut it all the way down to idle. It still appeared to be rising, so I turned the engine off and ran with only the port side for ~5 minutes. I restarted the starboard side, and the temp immediately started rising again. So I shut it down for ~7 minutes. But when I restarted that time, the temperature immediately started dropping to ~175°. I raised the RPM to 1,000, then 1,250. As long as I left it below 1,800rpm, the temp stabilized at 180° and stayed there all the way back to our home port.
It was then that I'd had enough. These engines are great, but something had to be done about that OEM engine oil cooler. Fortunately, I had two oil coolers from the 400hp 534 cubic inch twin turbo and intercooled Super SeaMaster engines that came out of my big project boat, a 1969 Chris Craft Roamer 46. I had them reconfigured so the hose fittings were facing the right direction for use on our Commander, and set about finally resolving the overheating problem on this boat.
Super SeaMaster oil coolers reconfigured for the Commander 42
The Super SeaMaster oil coolers are 3" x 12" overall, which yields 2x the cooling capacity of much cheaper 2" diameter marine oil coolers. This should work a lot better than the stock oil pan cooler.
Replacing existing oil hoses with new ones...fortunately, I had replaceable bronze fittings to work with
In the original configuration, the oil hoses go between the remote oil filter and the filter adapter on the block. I'll re-route them to first go through the oil cooler.
The new hose is installed in the reusable AN8 flared hose end that came on the Super SeaMasters.
The original raw water pump directs the hose straight back to the Chris Craft oil pan cooler
Raw water pump and hoses to the oil pan cooler removed.
The new (old) oil cooler in place
New (old stock) oil cooler installed and ready to run
The raw water hose runs straight from the new cooler back to the 90° turn up to the gear cooler, bypassing the OEM oil pan cooler entirely. I took the boat out and ran it up on plane (3,600rpm) for 15 minutes and, for the first time since we've owned the boat, the starboard engine didn't run over 180°F.
Fast forward to July 2021, and the same problem manifested on the port engine. The irony is that we'd never run the boat on plane since we got the boat in 2011, and even a semi-clogged OEM oil cooler can pass enough water to keep the engine from getting hot at lower RPM. But after doing the valve job on both port and starboard engines in 2021 and solving a longstanding fuel starvation problem (electric pumps can't pull enough fuel for the 427s), the boat was finally performing, speed-wise, as Chris Craft intended. But the clogged oil coolers just couldn't keep up with the extra heat generated at planing speed (3,600rpm).
Since I'd had both gear coolers from our 1969 Roamer 46 repurposed to fit the Commander 42, I decided to bypass the OEM oil cooler on the port side and be done with it. But there are some notable differences between port and starboard engines, the biggest of which was that the starboard came from the factory with a remotely mounted oil filter while the port side uses an off-set filter. For the starboard side, I only had to replace the remote filter feed and return copper lines with hose. For the port side, I needed a remote filter adapter so I'd have something to attach the feed and return hoses to.
I bought a Derale Cooling Products Oil Filter Adapter (PN 25770), four 3/8" hose fittings, four small hose clamps, and 1-1/4" hose clamps for the raw water hose. I had plenty of leftover hose from the starboard oil cooler install.
The oil filter on the port engine is mounted conventionally (threads up) but with an adapter that moves it forward compared to automotive applications. The marine version needs to be as narrow as possible to fit between the stringers.
There's plenty of room to add an oil cooler sandwich adapter between the oil filter and the base to which it attaches.
This is the Derale oil filter adapter pn 25770. It routes the oil out one port, to the oil cooler, then back via the other port, after which it goes through the filter, and then returns to lubricate the engine. There are other sandwich adapters that have temperature valves that don't open the ports until the engines reach some preset temp. But this is a boat that will mostly be run when it's warm out and cold oil isn't much of a concern.
The second oil cooler was ready to install anytime.
Derale oil filter adapter is installed, along with the oil feed and return lines. The adapter is held in place with a hollow threaded fitting that screws onto the fitting the filter normally attaches to. The Derale instructions didn't say anything about using thread locker, but I used LockTite red to make sure the fitting doesn't come off when the filter gets pulled for annual oil changes.
Figuring out where to put the oil cooler was a challenge. I've got aftermarket fuel filters that were in the way near the engine, so I had to locate it just forward of the engine bay.
Next, I repurposed the copper raw water line and attached it to new 1-1/4" double wall hose. The copper tube originally attached via short hose to the raw water pump outlet, which is on the outboard side of the port engine. It crossed the front of the engine before taking a 90° bend pointing directly at the EOM oil cooler that's attached to the oil pan. Since I'm completely bypassing the OEM cooler, I'll have a short hose connect the raw water inlet of the gear cooler to the copper line, and the new hose will go forward to the outlet of the new engine oil cooler.
Accessing the OEM oil cooler outlet hose and clamp is extremely difficult for a full-size American male. Fortunately, the clamp was oriented with the screw head facing forward. A 5/16" socket and a few extensions allowed me to reach it and loosen the clamp.
I took this shot from the space just in front of the starter looking back toward the OEM oil cooler and hose that goes to the marine gear cooler. Note that there is very little space between the hose and the stringer. In fact, there's less space than the OD of the hose. It's a real bear to remove.
The red arrow points to the deteriorated hose clamp that attaches the hose from the OEM oil cooler to the marine gear cooler. There's no way to get at it easily. The starter is in the way on one side, the stringer is in the way on the other, and the rear gear mount is in the way on the backside. I ended up pressing my back up against the rear ER bulkhead and using a 1/4" drive 5/16" socket with my left arm going over the exhaust and under the gear mount, then blindly feeling around until I finally got the socket on the clamp screw.
It easily took an hour to get this clamp and hose off. It would have been much easier if the engine was on a bench, or if the exhaust system and heat exchanger were removed. But that'd be a lot of work just to replace one hose. The Chris Craft engineers were obviously not even thinking about future maintenance issues when they came up with this compact marine propulsion unit.
But once I got the hose off, installing the new straight section of gear cooler hose with a new clamp was easy enough. The copper tubing with the long section of hose pointing forward slid into the new marine gear hose easily, and I double clamped it.
The 1-1/4" hose connecting the new oil cooler to the gear cooler is double clamped and ready for service. After a 10 minute test run in the slip, I found no leaks. I'll take the boat out for a spin soon and post a video.
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