engine started overheating. replacing a thermostat didnt help, engine will drive on road fine, then after 1/2 hour temp will climb. i always immediately shut it down when the temp climbs, then let it cool and it is fine. i cant duplicate it in the shop. coolant has been purged of air, one time it overheated it blew 600cc of coolant into the bottle. am i looking at a head gasket?
bob

 

Normally, with the car cold, you can run it without the radiator cap. If there are bubbles, then your head gasket is failing.

Never open the radiator cap when the car is hot as hot coolant will splash everywhere and might burn you.

 

Are your cooling fans working? The main fan is temperature controlled and should come on when the engine heats up after starting the car and the coolant temp reaches 190- 200 degrees F. The A/C fan should come on immediately when you turn the A/C on. The fan circuits are protected with fuses in the fuse panel under the dash. The A/C fuse is #10 and is 15 amp. The main fan is in the same location and is #30 with a 30 amp fuse.