06-24-05, 08:09 AM
Is it normal for the coolant reservoire to fill back up with coolant while the car is cooling off? It has not overheated but when I came home, I opened the hood and the coolant was bubbling (small bubbles) and going from the radiator back into the white plastic holding tank.
Maybe a little, but when hot it expands into it, then when it cools, a suction forms and the rad caps opens and it pulls back and keeps the radiator full. Now if it boils over into it when the engine is off, I would have more concerns.
It will allow coolant back into the resovoir when it exceeds cap pressure (16 psi on most GM). IT might do that when a hot engine is stopped and the temps climb. It is critical t make sure you have proper coolant concentration. Too little antifreeze and it will boil when the pressure drops and the temp is still up. Too much and it will not transfer a sufficient amount of the heat. 100% distilled water is best to transfer the heat, but it boils too easy. Under 16 psi pressure water boils around 225 degrees. And if you remove the pressure (like the cap) it will instantaneously boil and throw coolant in your face. It isn't fun. I was a dumb 16 year old and learned that one. No I didn't get hurt, but I learned....
If it fully boils over at engine shut off, and coolant concentration is good, then I would be concerned about a bad head gasket allowing combustion chamber pressure into the cooling system.
06-24-05, 01:53 PM
There shouldn't be any air in the system unless it has been opened, or has a leak. Once the engine has been run and cooled a few times, all the air should be bled out through the overflow tank. Then there shouldn't be any bubbles coming through. So if there is, I'd suspect a leak, or like he mentioned a headgasket that's letting air into the cooling system.
Personally I like to keep cap off till thermostat opens, then once open, rev engine to 2500 rpm or so, and add liquid, while maintaining rpm, then close cap and let it idle. That is about as full as it gets.