I have just purchased this Lumina with a 3.1 engine. It has an overheating problem. Have had the head gaskets and intake gaskets checked. Have changed the thermostat and bled the coolant system. The car will drive home fine, heat normally, hot air will come out of the vent. Then the next time in the car, the temperature will shoot up to near 260 degrees (it may radically fluxuate up and down), hot engine light comes on, low coolant light will come on and NO hot air coming out of the vent.