Chevrolet Beretta Forum : “Pressure building in cooling system”

Pressure building in cooling system

I have a 1996 beretta with a 2.2 engine. The problem I have is that air pressure is building in the cooling system. I have checked the head gasket and its ok. There is no evidence of antifreeze in the oil, or in the cylnders, and it is not steaming from the tail pipe. It is not leaking antifreeze, and I have not seen any puddles where the car is parked. It does not overheat at idle, but will heat up when being driven. When it does that and I bleed off the air, it works fine for a while, until the air builds up again. I am also noticing a water rushing sound from the heater core area when engine is cold, but as far as I can tell, the core is not leaking.