The Stovebolt Site Forums The Parking Lot Big Bolts My '51 4400 Overheats!

Last year, I had the engine pulled and partially torn down. The crank and pistons remained in place as they were all in good shape according to the mechanic. The water jacket was flushed out with a pressure washer and I had the original radiator rebuilt and installed a new thermostat. The main seals were replaced which the mechanic thought were a bit tight but also thought they would loosen up during operation. Last summer, I drove it to his shop on a road with a 45mph speed limit and while I don't think I was going that fast, the engine overheated on the short 5 or 6 minute drive and I lost a bit of coolant. My drives since then have been only on roads with 40mph limits or less and short drives at that, including my towns Memorial Day parade which of course was just creeping along while the temp remained below 180 degrees. Then a friend offered me a bunch of hickory logs for free but I would have to drive about 40 minutes on roads that had 40mph posted limits except through a couple of towns were the limit was 25. Everything was fine until I got to one town about 25 minutes away and during stop and go down the main drag I noticed the temp creeping up a bit. I got to the site where the logs were and left the truck running while my friend loaded the logs with his excavator and when I got back in the truck, I noticed the temp was up above 200 degrees. As I got back on the road, the temp began to drop as I drove along at 25mph or so. I made it home with the temp hovering somewhere between 180 and 200 degrees. The mechanic has suggested adding a fan shroud or an axillary electric fan but I think the it should maintain the correct temp with the factory equipment as the truck is essentially stock. I do know that I have some exhaust leak at the manifold gasket which needs to be corrected and wonder if that could be a source of the problem. Is it possible that the water pump doesn't pump enough water? We do plan to correct the manifold gasket issue first but does anybody have any thoughts on where the problem may lie? I appreciate any suggestions!

If it's the original water pump I think that's would be next, That's about the only thing in the cooling system that you haven't changed. It didn't have a shroud or extra fan when it was new.

I am going to start by saying it sounds like you do not have a problem.

Thermostat set MINIMUM operating temp - which is most likely 180

Internal combustion engine needs to run hot - otherwise a normal cooling temp is 190 to 210 assuming you are using 50:50 mix for coolant.

Engines can run much hotter with other coolants

Internal combustion engine is a thermal engine, with very low mechanical efficiency - best case for a modern engine is that only 47% of combustion engine gets converted to mechanical energy, the rest becomes heat energy

When your timing, mixture or compression is off/wrong, efficiency drops and you make more thermal energy to the point of exceeding what your cooling system can handle - so you begin to see temps exceeding 210

This of course assumes cooling passages, radiator, water pump and thermostat are working correctly.

Also - very few temperature gauges are accurate

In addition, perfectly normal to puke out some coolant since it expands when hot - basically it needs to set it operating level after an initial fill.

Fan belt slip at idle can cause rise in temp. Fan is only needed when vehicle is not moving. Retarded timing can cause rise in temps at idle.

I set my timing on my 235 between 5 and 10 BTDC with a timing light

The 51 cooling system will either have a "zero pressure" cooling system, or possibly a 4 pound pressure cap. Each pound of pressure raises the boiling point of the coolant 3 degrees at sea level, somewhat less at higher altitudes. Adding more cooling system pressure might prevent puking some coolant out, but the system is probably overfilled. It could also cause leaks, especially at the heater core. If the coolant isn't getting to a rolling boil and puking lots of coolant the engine isn't "overheating". A 4 pound cap will raise the boil-over temp to around 220 degrees. If you add a fan shroud, be sure it only covers the fan blades halfway. Fully enclosing a fan inside a shroud can actually reduce the airflow. Electric fans are a joke- - - -how many full-grown airlplanes do you see with electric motors driving the propellers?
Jerry

I live in Florida and the temps. in the summer average 90 degrees. When I put my 235 together I used a 160 thermostat and have a 0 pressure system. It never go's over 160 degrees unless its sitting still idling.

Thanks for the replies! I do think I have a problem as when it gets hot, it spews the 50/50 coolant out and less coolant means more hotter! It does not have a heater so there is no problem with that and it is a zero pressure system. I'm going to start with the exhaust manifold gasket after the mating surface of the manifold is planned flat to remove pits etc. Then I guess a water pump if the gasket does not fix it.

What was the temperature rating of the thermostat you installed? Was it 160 degrees, as Chris mentioned, or did you put in a hotter one? Maybe that's contributing to your issue?

I don't recall what thermostat was installed but as mentioned, the temp typically runs about the 180 degree mark. My 1950 3600 with the same engine does not vary much from the 180 degree temperature so I believe that this thing climbing to the boiling point is indeed an issue.

Power wash the radiator if you haven't already. Power wash from the engine bay out the front toward the grill as best as possible. I wouldn't be surprised if it's a crud build up that has formed blocking air flow.

The radiator is as new that was recently recored. There is no crud in it.

Gazz Why don't you put your themostat on the kitchen stove,see if it's working right. Foreign parts like we all suffer with can be problematic. Also do you have the big radiator,my 51 6400 big radiator outfit runs 185 degrees enen in 95 degree heat 50/50 coolant.

Try connecting the upper and lower radiator hoses together with a piece of exhaust tubing to isolate the engine from the radiator, with a tire valve stem in the tubing. Put 10-15 pounds of pressure into the cooling system and see if it drops over time. It's beginning to sound like you're dealing with a leaky head gasket or a cracked head that's letting combustion gas get into the ccooling system. If the pressure drops, pull the spark plugs and spin the engine with the starter. Coolant will probably squirt out of the cylinder with the leak if it's there. You might also be able to listen to each spark plug hole with a length of tubing used like a stethoscope and hear an air leak if the pressure drops quickly.
Jerry

Gazz Once hit a snag on a Pontiac,just happened to see a mouse nest in the block water jacket. Found out they can build those in there in short order. Also once saw an oil filter canister a guy brought in just full of some kind of fiber ?? Discovered an earlier cam installer had left one of those double shop rags in the valley,we hooked it with a wire hook and pulled it up in the oil fill pipe. Big surprise for the local chevy dealer.