Coolant leak 2006 pontiac grand prix

SOURCE: 2006 pontiac grand prix vary little or no heat

Are you sure you got all the air out of the cooling system? Air pockets are very common problem when you do any work to the cooling system. An air pocket will do what you discribe.

SOURCE: Oil light flashing, last oil change 7 wks ago

I belive they didn't reset the oil light timer. I belive the sequence is 1. key on (not acc with engine off)
2. step on the brake pedal 5 times within 10 seconds. 3. key off. 4. start car. 5. check if the light went out. you may have to try it a few times to get it.

SOURCE: 2004 GTP Grand Prix overheating in slow traffic

Are the cooling fans coming on during normal operation? If your ac works turn it on and see if it overheats with ac on.If it does not overheat the fans are not operating properly under normal operating conditions.The ac will force the fans on. What you can do to start is just let the car idle in park and see if fans will come on normally. The coolant temp should reach 200-210 before the fans will come on. Make sure the air is off at this time. If we can verify the fans are working or not working properly we can go to the next step. Let me know what you find out.

SOURCE: 1996 Pontiac Grand Am overheating

If its the 3.1L it could be your intake manifold gasket , the material used for the gasket does not react well with GM's Dex-Cool antifreeze. The leak may not be apparent at first, but I would pressure test the cooling system. If you look at the front of the motor by the belts , try to peek down at the intake manifold and check for slight seapage to an obvious leak.

If its either of the Quad-4's they were notorious for heads warping or cracking.

SOURCE: 2004 Pontiac Grand Prix OVERHEATING!!!

Have you shop perform a "leakdown test." You probably have a bad head gasket )or a leak in the gasket).