VCCA Home Forums TECHNICAL - 1945 AND NEWER 1949-1954 Radiator Pressure

I had the radiator redone with a bigger and stronger version on my 50 Chevy Powerglide. The standard Harrison radiator required a 4 lb pressure cap. When I use this low pressure cap on the new radiator the pressure starts to overflow dump almost immediately. I talked to the shop that did the radiator and they said I could go up to 13 or 16 lb pressure cap. My question is; does anyone know if the tank that the transmission oil cooler lines run to, will take that kind of pressure? Should the transmission oil cooling tank breaking open be a concern?

Your problem indiactes that you have another problem.The "dump" -overflow????...should not occur even with no pressure cap.
When using a modern thermostat in an older car some times its necessary to drill a small hole in the valve of the thermostat.This allows the pressure to equalize and the thermostat to open properly.
The weak point in the system is usually the core itself.The cooler is made quite sturdy unless it is rusted and weakened internally.The 1954,which used the same cooler had a 7 pound cap and it posed no problems.

But all in all installing a higher pressure cap will actually make things worse as it will place more pressure on the thermostat and further delay it opening and increasing the dumping problem....and it is not fixing a problem.

My '50 three speed didn't have a pressure cap and it worked fine...

I drilled a hole in the thermostat and installed a "overflow tank." We will see what happens.

Maybe you have overfilled the radiator. It will overflow no matter what pressure cap you use if this is the case as the heated water expands. The pressure cap is only to increase the boiling point of the water and if the water is boiling soon after startup, you have engine problems. I use a catch bottle so I can monitor the amount of coolant loss from the overflow and add it back to the radiator as needed.

In 1950 the PG had a 4 lb.cap and the stick did not have a pressure cap.If the vehicle was operated under "heavy duty" conditions Chevrolet said a pressure cap could be installed on the stick shift cars.Odly the 1948's all had a pressure cap.Chevrolet said the radiator on a 1949 cooled better and it was not necessary.The PG dumped more heat into the cooling system due to the trans. cooler so they all used pressure caps.In 1952 the pressure cap was again used on the sticks as the core was reduced as far as cooling ability was concerned due to material shortages caused by the Korean war.

My 1950 PG had the original bellows type 180 deg. thermostat in it when I got it.The 180 came with the heater and permenant antifreeze is required.I put a modern 180 thermo in it and when the engine warmed up the temp. gauge would go ut to 200 deg. before the thermo. opened.After that it stayed on 180.Seeing I use and abuse it in hot weather I installed a 160 thermo and a Chevrolet accessory over flow tank.If its gets a head of steam up in mountain driving it won't flow over.Never have a problem in normal driving.....it will get its real test in Colorado next year.

When filling the radiator when cold the coolant level should be kept lower - just so it can be seen in the tank.When it gets up to normal and expands there will be enough room and it won't puke.

The hole I drilled in the thermostat seem to have done the job. Thanks again everyone.