VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 Overheating

I still haven't kicked this problem with the ”˜38. I back flushed both the radiator and the engine and left out the thermostat. There was no resistance in either case and the water ran clear in a couple of seconds. When I buttoned it back up it appeared as if the problem of overheating was gone. However, after a couple of days of working with the car the problem is back.

When the car is running the temp stays about 190 or so but as soon as I stop and turn off the engine, the temp rises to 212 and I get a small amount of boil over. What I don’t understand is how stopping the engine causes the temp to rise unless there is a portion of the engine that is not getting good coolant flow or is completely uncovered of coolant so that when I stop the engine, the coolant rushes in and boils on these hot surfaces. The water pump is new and looks great, although I know that is no indication of actual performance.

If I run the engine in the garage for over 20 minutes the temp will rise to 212. I have retightened the head bolts, re-gapped the valves, checked the engine timing (it’s good), checked the vacuum (steady at 17-20 at all speeds).

Right now it is still relatively cool outside so this problem is only going to get worse as the season progresses. If you have any ideas, please let me know.

Brian

I had the same problem with my 37 so I just went and had the radiator recored and have had no problems since. Runs about 180-190 and after I shut it off no more boil over's

There's probably a zillion possibilities I'm sure you'll hear more about. I had a similiar problem with my '39 and the best thing I ever did was to have my radiator recored with a modern core using the original top and bottom tanks so I looks original (probably won't pass inspection at a judging) and it really cooled everything down. It cost me about 300.00 in Denver. They said that the original cooling tubes get choked off and can't be properly cleaned. That was my solution...hope it helps.
Best wishes,
Chuck

If the timing is off, it can contribute to heat problems. Might be worth a check.

I agree with garbo. My '41 was overheating especially in Parades , etc. I had a modern core put on my top and bottom. $200.00 here in Missouri. While I was at it I put in a new water pump and thermostat. Now my '41 runs on 180 degrees and does not boil over. 90% of the people , judges or others can't tell the difference in the looks of the new core.
Good luck JIM

With that much of an overheating problem there is something very wrong.Would pull out the core and have it flow-tested and go from there.A stock core in good clean condition would not heat up as easily as yours does.
If it was OK for a while after flushing rust may be flowing out of the water jackets and plugging up the core.Very common.

Thanks, I was looking for something more like "You forgot to adjust the Fitzer Valve dummy, just make a tiny adjustment and everything will be okay". Not "You have a catastrophic failure and its going to cost you a lot of money and time". I had enough trouble getting the hood on the first time.....

Brian

PUT THE THERMOSTAT BACK IN YOU NEED TO RESTRICT
THE FLOW SO THE COOLANT STAYS IN THE RAD. LONG
ENOUGH TO COOL DOWN.

I lived exactly what your going thru, I wish I could tell you one thing to do, but here's my story, I had the radiator core replaced with a 4 pass core, rebuilt water pump, had the head rebuilt, put a 160 thermostat in, tuned per the manual - timing, plug and point gap and flushed system with drain-o (this I read about on this site), I don't believe the temperature has been over 180, including trips to the desert in temps above 100 degrees. I have a 1940 stock 216, have had no heating problems in over 10 months. I am willing to give you more details if you E-mail me (whmarquis@aol.com) Good luck.

i agree with alot of the other responses. if you are running your original core still, you would be better off having a new core put it. over time no matter how well you maintain your system it will still build up scale and eventually close up completely. also most engines will rise in temp after being shut off before dropping again due to the system not moving coolant through the engine. as far as anything else to try i dont know what i could drop in that wouldnt repeat what everyone else has said already.

also dont let the grease monkey label fool you. ive been a mechanic in the coast guard now for 7 years and ive run into alot of issues with our antiquated navy hand me downs. youd be surprised what a cowboy can rig up to get his boat back to shallow water . cooling casualties included.

In general the coolant temperature will always rise just after shutting an engine off. The reason for this is that the coolant is no longer circulating. The much hotter engine heats the coolant which cannot get rid of the heat because it's not circulating through the radiator.

I was going to give it a good evaluation this weekend but I called the local radiator shop and they quoted around $350 so that seems about right. Hopefully, if it comes down to that, I can get a core that looks like the one I have. I might even have them rod out the old core first to see if that solves the problem.

Thanks for the help,
Brian

Replace the thermostat,water pump and have the rad. re-cored There is no sense in messing with ruining an engine..

The above is a very common misconception. I don't know how it got accepted by as many people as it has but it is not what is happening. A very common problem is air entrainment. That is air bubbles being drawn into the coolant typically past the shaft on the water pump. It can be drawn past hose connections also. Since air has a viscosity much lower than water or coolant it will be drawn in when water (or coolant) does not leak out. If any moisture is noted around the water pump rest assured that water is being drawn into the non-pressurized cooling system. This air expands when heated forcing water out the overflow and also reducing the heat capacity of the coolant. When the engine is stopped or slowed the bubbles can expand resulting in what might be thought as boiling.

Now for the reason that a restriction in the upper radiator hose appears to work. The restriction increases the pressure in the engine cooling passages keeping the bubbles smaller. But when the water pump stops or slows the pressure is reduced which can result in expanding sized bubbles. An overflow/makeup system can be a significant help in maintaining coolant level, allowing some air to be removed without losing coolant. If the tank is mounted high up into the engine compartment, piped to the outlet of the overflow tube and the radiator cap seals to the top of the radiator then it will work just fine.

Just trying to set the record straight and not trying to be critical of anyone.

Bigbth
An easy way to test radiator flow with engine running watch the bottom radiator hose and open throttle to approximately 2000 rpm for a 10 to 15 seconds. If the bottom hose shows any sign of distortion the radiator is at least partially blocked.
I recently had a friends vehicle that totaly collapsed the bottom hose at idle, the radiator flowed water through 3 tubes only.
Tony

Reducing the flow through an air cooled radiator will, without a doubt, result in lower temperature of the exiting liquid, if the inlet temperature stays the same. That's the problem. When you slow the flow through the radiator to increase the amount of heat taken per unit of liquid, you also reduce the flow through the engine that causes a rise in the temperature of the liquid leaving the engine. In this case the heat source is greater and the contact time longer than the cooling side, so you end up causing a net rise in the average temperature of the cooling system. The faster the flow of coolant the closer the system will come to a single temperature

I’ve seen lots of pump and there is no way the water pump on a ’38 is generating the vacuum at the shaft necessary to pull air into the system. Based on the design of the pump I’m surprised it even moves coolant. Not to mention, with a thermostat in the line it runs deadhead without any ill effects. Although I will check the lower hose this weekend to see if there is any deflection at all at higher speed.

It’s not that I don’t understand radiators and cooling it’s that this system is not behaving in a manner consistent with the design, even with flaws. If the radiator has plugged tubes the temperature of the engine should rise to a higher level than is normal, the liquid should expand and overflow, but it should be consistent and repeatable. This cooling system over heats one day not the next, boils over when you stop but when driven is well within normal range. I know that the air temperature and humidity will affect the cooling rate, the way the car is driven will affect the heat load, but I wouldn’t think that it would be this erratic. IT’S driving me MAD. Not that it would have been a long trip…

Brian

Brian:
I had a simlar overheating problem with my '35 (short water jacket) that I am determined to fix once and for all. I bought a NOS radiator, but thought that I would go the extra step of pulling the head just for a 'look see'. Glad I did...I found lots of crud in both the head and the block. I pulled the engine this week, removed the freeze plugs, rodded out both the head and block, then hit it with my pressure washer. All kinds of chunks and debris came out, include a core rod probably from the original casting. I have a few pictures I'll send you that show the mess. I can't wait to put her all back together and see her run cool!

Coach

Just an interesting note that should get a few of you thinking. In my former life (pre-retirement), I spent many years in the automotive chemical department of a major chemical company. My job was to provide technical service to customers with heavy-duty vehicles and equipment. Cavitation in wet liner diesel engines was very common and not well understood. The engine companies and we did a lot of work to determine the cause and formulate a solution. Glad to report that the problem has been understood and generally solved.

A major focus of our work was the condition of the coolant and any contaminants. I will not go into details but we found air entrainment even in cooling systems pressurized to 15 psig. Three major sources were found. The top of the radiator with the air/coolant interface, especially with high flow rates resulted in extremely small amounts of air being mixed into the coolant. The hose connections, particularly with silicone coolant hoses produced higher levels of air. It is the result of flow past a change in the internal surface. The higher the flow rate (either laminar or turbulent flow) past an increase in diameter of the passage [such as then end of a pipe as it goes into a hose] the greater the pressure drop at the connection and the more likely air will be drawn between the pipe and hose connection. It happened even when no evidence of leakage. Then there was the water pump. It was by far the source of most of the air. I could write many pages on the why and how even in a pressurized cooling system that air can be drawn in against that pressure head. Doesn't seem logical but trust me it happens. And with non-pressurized systems it is much more prevalent.

One of the major reasons to go to the coolant recovery systems used on all modern vehicles is to minimize the entrainment from the coolant/air interface.

Just one more comment, if there is no reduced pressure at the impellor of a water pump then the pump will not function. The faster the rotation the more the pressure is reduced at the inlet and the higher the outlet pressure.