When I drive the car it runs in the 180 range but when its stop and go like in town in starts to get above 210. I have replaced the thermostat and added coolant. Sometimes it doesnt even read that hot when when I park it starts to bubble out of the over flow. I just added coolant and started the car and turned the defroster all the way on to try to get all the air out of the system but I heard its really hard to get the air out. Just wondering if anybody has had this problem. I also just replaced the coolant temp sensor.

 

210*F is not too hot. Pretty normal for the temp to get there when stopped or moving in slow traffic. GM meant it to run there - that's why its the midpoint of the guage. The fans don't come on until 226*F (low speed) and 235*F (high speed).

There is constant flow through the heater, no flow control valve. Turning the heater on does nothing to the flow, turning the defroster on turns the A/C on.

As far as the bubbling, make sure the cap is holding the required 18psi.