Help me get my brain around this cooling issue.

Greets,
Over the past few days, when I arrive at my destination and shut off the car, the coolant violently boils over into the overflow tank. While driving, the temp gauge reads pretty much as it always does. While idling, I don't see any boiling over, only once I shut off the engine. The top radiator hose from the radiator to the engine blows up like a balloon.

I thought it might be a weak radiator cap, so I replaced it with a new 16lb unit this morning, and low and behold, no boilover when I arrived at work after 50 miles of driving. However, this evening, after I arrived home, it started again after I shut off the motor. I restarted the car, and let it idle, and the spitting out of the coolant subsided, only to continue when I shut off the car again.

Any ideas? I assumed that if it was a head gasket leak, that it would cause issues while running as well, correct? I have a pretty new 180 deg thermo, and removed and inspected it the other day.

Regards,

Gary

Thanks guys,
It didn't boil over this morning either. I know it's about 15 degrees cooler in the morning than the evening, but I am not sure this would be a major issue, as it is still in the mid 70's - 80's tops.

Question regarding the burping: The presence of air bubbles could cause this issue how? Is the air pocket blocking the flow of coolant, and thus preventing the guage from reading correctly?

Regards,

Gary

Hey Chris,
Started a week or so ago. Nothing was done to the car. BTW, It hasn't boiled over since I posted this question. Possibly, if it was indeed an air pocket, that it passed. Very odd...

Thanks ,

Gary