how the rad cap. there is only a few places air gets into your systemm.and what way it is. i needs to be fixed. air just doesnt appear in your coolant system. i dont care how hot you get it. if it boils over when it cools it will turn back to liquid. but it if doesnt that means you have a leak somewhere. and needs to be addressed. head gaskets. hoses. and heater core and thermostate housing are the most common areas. look for leaks maybe and burp the system. if the hoses feel soft when the car is warmed up.