VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1933-1936 36 engine running hot

A little background. The engine is in a 36 1 1/2 ton fire truck. The original engine ran cool all the time. Block developed a crack and I had the chance to buy a new, in the box 1936 NOS replacement engine, complete with head, pan, and valve cover. The guy I bought it from said he would throw in a good manifold and carburetor, starter, generator, bell housing and transmission making it a truly a complete engine. I did open it up to check the condition of the crank to see it hadn't rusted. Lubed it with Clevite rebuild bearing lube. Again, everything looked perfect.

OK, from day 1 it ran hot. Same radiator as the other engine. I had been able to drive in a slow parade at 100 degrees and the engine would never go over 180. This engine runs at 180 idling on 60 degree day! The radiator had a new core, so not a plugged core. Last fall at the VCCA Southern tour I had trouble keeping anti-freeze in the radiator despite never being over 80 degrees. The fan belt is and always has been tight, so no issue there.

Today I began tearing it down and comparing this engine with the previous engine. Here is what I have found so far.
1. The radiator is perfectly clean, not a spec of rust and water flows faster than I can run it in with a 60 PSI water hose. Turned it upside down on ran water from the bottom up, not a spec of rust came out the top. Conclusion, the radiator is clean, but to be sure I am taking it to the radiator shop for a complete test.
2. It has a 1936 water pump (as evidenced by the wide impeller)which I bought from FS a couple of years back when someone suggested it may have a 1935 water pump with the slim impeller. Even though it is supposed to be a new pump, I have to continuously tighten the packing or it leaks around the shaft. Wonder if it is sucking air around the shaft? By the way, it doesn't lose water then get hot, it gets hot then pushes water out.
3. I run 50/50 mixture of permanent anti-freeze summer and winter with anti-rust. Using a flexible light I inspected the inside of the block, it is a clean as it was from the factory. Flushing with high pressure water yielded no rust or crud at all.
4. I measured from the front of the block to the cast in baffle on both engines, they measure within .020. I measured from the flange of the water pump to the back of the impeller and compared that with the measurement from the front of the block to the center of the cast in baffle. Have about .190 clearance, but if I measure to the raised rim of the cast in baffle, I have only about .020 clearance.
5. I decided to check valve timing, removed timing cover and found the timing marks properly aligned.
6. Decided to double check the valve timing by using a dial indicator on the head with the tip touching the exhaust valve. At about 1 to 2 flywheel teeth from TDC EXHAUST STROKE, the exhaust valve is fully closed. At about 1 to 2 teeth after TDC EXHAUST STROKE, the intake valve just starts to move. I conclude that the cam is properly timed to the crankshaft, verifying that the timing marks are properly positioned.
7. I wondered if perhaps the heat riser was stuck, and without thinking how dumb I was being, I removed the carburetor to look and see if it was open or closed and movable. Of course I couldn't see the heat riser and felt rather silly about such an obvious mistake.

BUT HERE IS WHAT I DID FIND AND WONDER IF THIS IS THE SOURCE OF MY PROBLEM! When I looked down the throat of the intake manifold just below the carburetor I noticed something I had never ever seen in a Chevy 6 intake manifold. There is a sleeve of something like pheonalic pressed into the throat. That reduces the diameter of the throat from 1.500 to 1.400. Then inside that sleeve is a tapered sheet metal sleeve that measures 1.400 OD at the top then tapers down to 1.080 ID at the bottom. It is about 2 inches long top to bottom. Now I am wondering if this has been causing the engine to run very lean, thus hot. I can't imagine how it got in there and what it's purpose is? Presumably it is acting as an RPM limiter, not allowing enough fuel/air mixture to over rev the engine?? Or, did someone decide this was a way to improve gas mileage? By the way, the manifold wasn't attached to the engine, they man I bought the engine from said he would throw it in as a bonus and I simply didn't notice the thing until tonight.

I just did a calculation of what restriction that cone provides. At 1.5 inches I would have 4.71 Square Inches of area just below the carburetor. However at 1.080 at the tip of the cone, I would have only 3.39 Square Inches of area, or a reduction of about 28% in area. I seriously doubt the engine was designed to run with 28% less manifold area! But, would that make it run hot? I kind of suspect it would.

Any input or other suggestions as to what else I should check while I am into this mystery would be appreciated. I don't want to jump to the conclusion that the cone is the problem or only problem and have to go back into the engine later.

Ron

My first thought is that air being drawn past the shaft on the water pump is your major problem. It does not take a lot of air to reduce the amount of heat removed by the coolant. Is there any evidence of foam in the top of the radiator? That is a sure-fire indication of air or exhaust gas.

The restrictor you saw in the carb. to manifold insulator was used on truck engines to prevent the engine from being over reved. That is why a truck engine is rated at less horse power than a car engine. Truck 72 HP and car 79.
The 1935 water pump will not bolt up to a 1936 block.

Ron,

A few more things to consider:

a. The thermostat may be sticking. Replace it.

b. The bottom hose may be weak and collapsing when hot, etc.

c. The head gasket may be blown and leaking hot compression into the water jacket. Trip the fan belt, take out the thermostat, replace thermostat housing, leave top hose off, fill with water to top of thermostat housing, start the engine and look for bubbles. Water should sit still.

d. Fins in the radiator may be stuffed full of bugs.

e. Rusted up back of block. While keeping the engine filled, use a high pressure air source and blow through the block at the rear petcock.

f. New engine is producing a lot friction getting the rings seated and, according making it run hot. Take on a round trip of about 100 mile at about wide open or so. That will seat everything. Otherwise, it just takes a long time, especially if just used for parades.

I would think the head gasket more than the other thing I have mentioned although the radiator, despite your finding so far, may be the culprit.

Good luck with it,

Charlie

OK guys, thanks for the suggestions. To answer some of the questions posed,
a. I do not run a thermostat
b. Bottom hose is in perfect condition, no restrictions
c. Compression on all cylinders is even, but will try the "bubble" test
d. Radiator fins are clean and clear of any debris
e.Block is clean front to back, when I drained the block, didn't need to clear any rust from drain port as you usually have to do to get the water to flow.
f. I said it was a new engine and it is, but I have driven this engine over 4,000 miles in all kinds of conditions, from long road trips to parades. Burns no oil so rings are well seated.

I am taking the radiator to the shop that installed the new core for a careful checkup, both inside and out to eliminate that as a problem.

I am suspecting the air past the shaft possibility. I had thought buying a new FS pump would have resolved the pump problem. Am considering removing all the packing and starting with fresh. Does anyone have a suggestion as to the best material to use? Obviously the packing in this pump is not suitable. I have to adjust the packing about every 250 miles to prevent leaks, but the other engine pump ran the 2,000 miles without adjustment and never leaked a drop the entire time. Sadly I don't know which of the six pumps I have is that one. I thought putting a new pump in the new engine was the way to assure me of a long running engine.

Thanks again for the input.

Ron

If there is any restriction in the radiator (I note you tested for that) the water pump is capable of moving more water than most rediators can flow and this can cause the hose to collapse (suck in) especially at higher engine RPM.
Tony

Ron, just a comment on the water pump packing:

I could not get my 36's rebuilt pump to quit leaking from around the shaft until I supplemented the packing on the pump side with a couple of wraps of round Teflon cord from the plumbing department of the hardware store. This is NOT Teflon tape, but a ROUND cord! It has worked leak-free now for about 4 years, and I've not had to re-tighten the packing nut either. Cheap fix--do it with the pump in place--and worth a try!

W.W.

On the Heat Riser....There is a counter balance weight located on the manifold forward of the carburetor. It is between the manifold and engine. Not readily see able from the side of the engine. In a position where you are looking "down" from the top...you can see it. You can move it with your figures up and down to see if it is working.

Thanks for the tip on the teflon cord. Re the heat riser, I pulled the manifold as I could see the weight as was pointed out and it is stuck in the up position, I.E. it is in the mode to heat the intake manifold all the time. However; when I took the intake and exhaust manifold apart, behold! The flapper had been removed, so it is always in the open position.

Radiator is in the shop being tested but he is a week back-logged, so will be a while before I get any diagnosis there. He did take a quick look and said that it looked remarkably clean inside and out, so doubt this is the problem.

Also sent one of my spare pumps back to FS for a rebuild. FS says they cannot get new pumps, so rebuild is only option.

Thanks for the suggestions and input.

The heat riser really will not cause the engine to overheat. If stuck in the hot position could cause over heating the carburetor and boiling the gas out of the bowl in hot weather.
If in the cold position poor performance in cold winter weather.
Does the core feel equally hot a over the entire unit?

Hi there,
I have read all the reply's with great interest.
I had a similar problem last year and nothing I did to rectify the problem worked, Until............

I removed the radiator to have it cleaned and it appeared to be in a clean condition anyway.
I put new gland packing's in the water pump and tightened to make sure that I was not sucking air.
I used some very expensive solution to clean the radiator and block water ways and water, a long complicated method was used as recommended by the Australian manufacturer, but sill over heating.

Finally, I had to pull the head, jammed thermostat, boiled motor and the rest is history, But.......

When the head came off, the majority of the water holes in the head were blocked, totally.
The holes are very small, yes very small and any obstruction would cause overheating at the stroke of a hat.

When I eventually found a new head to have reconditioned and fitted, the overheating problem vanished.

I had been advised many times on this forum to pull the head and have a look, but because it was a big job , put it off for many months of overheating, water pouring out of the radiator cap every time the engine warmed up.

I have also refitted a thermostat, Minus the center part, so that the correct flow rate down the radiator core is maintained.
I live in a sub tropical location and don't really need a thermostat to aid engine warm up in the winter months, so that's why I made the modification to the thermostat, (the cause of the disastrous blown head cracking and subsequent replacement).....

Peter

I agree with BlueyAU. That is the very same thing I went through. The Head has spray nozzles that are brass with small holes. These are designed to spray coolant on the "Hot Spots" in the head. This was one of the "NEW" designs by Chevrolet to prevent overheating. In addition to these being plugged by chunks of rust the holes going into the head from the block were almost plugged solid by chunks of rust. Most of it was caused by the head gasket that partly stuck out into the passage between the block and the head. The only way to clear this problem is to remove the head and clean both block and head.
After I did this she runs properly and dead on the temp she should. Never overheating.

Now would this be the same problem I'm having on my '47 216...?
Every thing look's fine but I have some overheating on warm days...

I would look at it after you have checked out everything else first. A lot of things can cause overheating as you already know. (Timing, Water Pump, Thermostat, Radiator, Hose sucking shut, etc.)But if you go that far I would have the head checked for hairline cracks at a machine shop, too.