Car overheating.. what could be the main problem?

Air in the system, worn water pump, cooling fans not working etc, etc. If the car blows white smoke or it is losing coolant all the time the head gaskets may be bad.

Most likely you have air trapped in the cooling system. With the engine cold remove the radiator cap and loosen the bleeder screw at the thermostat housing. Add coolant to the radiator until coolant comes out of the bleeder screw in a steady stream. It's also helpful on these vehicles to have the front of the vehicle parked so the front is angled upwards. On the 3.8L V6 symptoms of a blown head gasket are going to be the intake manifold gaskets. These engines rarely blow head gaskets but the intake manifold gaskets always fail! Is it overheating while driving or idling/slower speeds? Hope that helps! Jim