Ok my car is getting warm sometimes, only on long drives and mostly if I get on it..I have replaced the Thermostat,and I have checked the head gasket..( I was tlod to start your car without the cap on and let it run and if the water starts to shoot out the the gasket is bad, but if it just kinda vibrates witht the motor then it is fine, well that is what mine does), SO I am hoping this is my problem (radiator cap) Also when it heats up I can turn the heater on and it goes down to normal operating temp. almost immeadiatly..What could that mean? It is TOO hot to drive around with the heat on Thanks for any help you can give me..Also is there anyway to pressure test the cap?