Car overheating but not with Rad. cap off

Sounds like air is trapped in the cooling system. With the engine cold open the bleeder screw(s) and fill the radiator with coolant until you have a steady stream of coolant coming from the bleeder screw(s). It's helpful to park the vehicle on an incline with the front pointing upwards, like halfway in the driveway. If you have the 3.4L V6 there's a good chance you have a blown head gasket. These engines are notorious for blowing head gaskets. Hope that helps! Jim

That was it i opened the bleeders did like you said now no more overheating Thanks :D i just bought the car i was scared of head gasket too but there was no water in the oil.

That's awesome!! Thanks for letting us know!! I'm glad to help! My Niece had an '05 Impala and I have a '00 Grand Prix. I'm pretty familiar with these GMs. Enjoy your new Impala! Jim