vigorous boiling - water lost thro overflow

Mom wants her car back :(
Got new radiator cap. Flushed (I thought) radiator, filled & let set for 2 days. No leaks. When started, the water in the overflow bottle started running out. After water level dropped below overflow, (5-10 min) just blew bubbles, then water started really bubbling, almost erupting, water bubbled harder. Like water boiling inside bottle. Where's the air coming from ? What's going on?
'88 Caravan. - - - - - - Autogirl

It must be pressurizing somewhere. Take it to a mechanic.

sounds like you have a corrupted head gasket. Combustion chamber pressure releasing into the water jacket. Best thing to do is a cooling system pressure test, and a leakdown compression test. this will tell you where the problem is.

by pressuring up one cylinder at a time, you will be able to find out exactly where the air is coming from.

good luck