72 BB spitting from Reservoir tank

[Melissa N.]

When the water level is properly set, the car will still spit out water after the car is turned off. It isn't just the first time, but rather several times so that eventually too much water is spit out and then the car will run hot. The fan clutch; the radiator cap and the motor seem fine. The motor does not run hot when the proper water level is set.

The question then is whether or not the radiator, which clearly functions when the motor is running, is somehow responsible for the build up of temperature and pressure when the car is turned off.
Suggestions?

[Patrick H.]

Re: 72 BB spitting from Reservoir tank

99% chance of one of these two:

1. Radiator cap just doesn't work anymore.

2. Too much water, no matter what the level indicator says.

Replacement GM radiator caps (bought from GM, not the reproductions) are cheap enough to test #1. With #2, the coolant level will eventually seek its own compromise and stop spitting coolant.

Patrick

[Joe L.]

Re: 72 BB spitting from Reservoir tank

99% chance of one of these two:

1. Radiator cap just doesn't work anymore.

2. Too much water, no matter what the level indicator says.

Replacement GM radiator caps (bought from GM, not the reproductions) are cheap enough to test #1. With #2, the coolant level will eventually seek its own compromise and stop spitting coolant.

Patrick

Patrick and Melissa-----


There's a third possibility: this is a normal sort of thing for pre-1973 Corvettes. Anyway, I vote for this one. My 1969 small block required regular topping off of the radiator supply tank from the time it was new. Pre 1973 Corvettes are not the sort of cars that you can more-or-less forget about checking coolant level at regular intervals (like you can with modern cars). You will note that all 53-72 Corvettes have a coolant overflow hose from the radiator or supply tank. This hose is not there for "emergency relief only"; it's there for REGULAR use.

In 1973 Corvette went to a coolant recovery system. This eliminated the overflow condition because the "puked out" coolant simply flowed to the recovery tank and was recycled back into the radiator. If earlier cars not equipped with a recovery system only on rare occasion "puked" out coolant, I doubt very much that GM would have seen a need to go to a recovery system in 1973.

[Patrick H.]

Re: 72 BB spitting from Reservoir tank

I think the key is when she said that "it then overheats."

The radiator cap (original) on my 72 is not fully functional, and puked on me. It also over heated.

New cap, both problems gone.

Just my experience.

Patrick

[William C.]

Re: 72 BB spitting from Reservoir tank

Just another thought, is the car running water or a proper 50/50 water/antifreeze mix in the coolant? The mix has a higher boiling point than straight water as I remember, and Temperature will climb right after engine shutdown on any engine, but the BB especially. Don't miss Patrick's message on the pressure cap, 15 lb I believe on a BB, and from when I had my '72, it was very necessary to maintain control.

[Michael M.]

Re: 72 BB spitting from Reservoir tank

Actually the temp doesn't increase after the engine is shut off, the PRESSSURE increases because of the lack of FLOW through the engine. Change the cap, I know you want originality, so put it back on for judging, but drive it with a new cap.

[Michael W.]

Re: 72 BB spitting from Reservoir tank

Actually the temp doesn't increase after the engine is shut off, the PRESSSURE increases because of the lack of FLOW through the engine. Change the cap, I know you want originality, so put it back on for judging, but drive it with a new cap.

Not to be argumentative, but the temperature of the coolant does increase after shutdown due to residual heat soak back from the engine block. The increased temperature in turn raises the coolant pressure.

Try this- after a good long run in your car, turn the ignition on momentarily about 5-10 minutes after shutdown. You'll see the indication has gone way above normal. Of course it's only the coolant in the block that has increased in temperature, not the coolant in the radiator.

[Michael M.]

Re: 72 BB spitting from Reservoir tank

LOL....OK...OK.........check this out. If the engine is not running, it cannot create any more heat. I would agree because of the temperature/pressure/flow relationship, the coolant temperature may seem to rise when the engine is shut off, but it is reaching a point of equalibrium between the coolant and engine.

My advice is still to change the cap.

[John H.]

Re: 72 BB spitting from Reservoir tank

the coolant temperature may seem to rise when the engine is shut off

It doesn't SEEM to rise, it DOES rise; the engine castings continue to give up heat to the coolant, and the coolant isn't circulating any more, so its temperature rises, increasing system pressure. If the cap can't maintain rated pressure, nucleate boiling ensues at the hottest coolant/casting interfaces, overpowering the cap, and coolant "pukes".

Yup, change the cap.

[Joe L.]

Re: 72 BB spitting from Reservoir tank

It doesn't SEEM to rise, it DOES rise; the engine castings continue to give up heat to the coolant, and the coolant isn't circulating any more, so its temperature rises, increasing system pressure. If the cap can't maintain rated pressure, nucleate boiling ensues at the hottest coolant/casting interfaces, overpowering the cap, and coolant "pukes".

Yup, change the cap.

Yes. And, while the engine heat continues to soak into the coolant after the engine is shut down, the radiator doesn't do much, at all, to remove any of that coolant heat.