Overheating heat stop working

thermostat stuck closed? low coolant? coolant leak?

Coolant good how do I check to see if the thermostat stuck?

http://www.wikihow.com/Tell-if-Your-Car's-Thermostat-Is-Stuck-Closed

there is also another way to do it, but you have to remove the thermostat and test it in water..

Thermostats are cheap. Just replace it and see if your problem goes away.

On these cars Pontiac Grand Prix on that issue...There are coolant elbows...1 on top by the supercharger and one underneath the altenator...I just finished replacing Both but instead I went with the aluminum the newer stuff instead of going back with the plastic and all my overheating problems went away.