1940 Roadmaster pushing coolant

[Drakeule]

All:

It seems that my big block '40 Roadmaster pushes some coolant out of the overflow tube when I stop; I've read the article from the "Torque Tube" on this, and it claims this is normal?

 

My '40 Super never does this.

 

New 7LB. radiator cap installed; faulty bypass valve or maybe just thermostat to blame?

 

Thanks,

 

CD, Potomac, Md.

[billorn]

Did you leave the upper tank empty or fill to the top of the neck? It needs some expansion room or it will puke.

[Drakeule]

Never heard this! Should the upper tank be empty? Inquiring minds want to know.....

[EmTee]

If it pushes once (or twice) and then is happy, maybe it was just overfull.  If it regularly does this then I would check for a restriction.  Could be thermostat or partially plugged radiator core.  Does the lower hose have a spring inside to prevent it from collapsing due to suction?

[Bloo]

1 hour ago, Drakeule said:

Never heard this! Should the upper tank be empty? Inquiring minds want to know.....

Pretty much. The top of the tubes should be completely covered up, but not much more than that. It's true of most old cars prior to the 70s. Water expands with heat. It has to go somewhere. Some cars have a surge tank, a small tank under cooling system pressure to act as the airspace so the radiator can stay completely full. Others have an overflow tank (not under pressure) that takes the extra coolant from expansion and returns it later by siphoning when the engine cools. To the best of my knowledge a Buick Eight has neither and is going to require a bunch of airspace in the top tank of the radiator.

 

Edited August 13, 2023 by Bloo (see edit history)

[neil morse]

Do you have the shop manual?  On my '41, there is a line embossed on the upper tank under the filler tube that shows the proper coolant level.  As a rule of thumb (pun intended), stick your finger down the filler tube.  Just the tip of your finger should get wet.  

[nat]

     Fill it up.  Measure how much is required to refill it after a run.  Everything is ducky if it only takes the same amount, (a pint or quart), to refill each time.