Since you guys know alot about cars in general I am having trouble with my winter beater. I am having heating issues. The resevior is always full, just replaced the thermostat, bled the system, flushed the system. Now the problem. The car will heat up fine but after running a while it will start to blow cold air, then warm again and back and forth. If I shut the car off after driving it it will only blow cold air and then the water temp rises and it starts to boil over. I can crack the top let it boil over then start it back up and it will blow warm again. Mind you it is never really hot just pretty warm. What should I check next I really don't know. Oh by the way the car is a 1990 Eagle Premier Please help:wallbash:

 

Sounds like your heater core is going bad.

 

Thanks Lance I will replace the heater core but if anybody else has some in put it would be much appreciated