Mitsubishi Repair: 99 Galant, coolant temperature sensor, engine coolant temperature sensor

Question
Hi
I have a '99 Galant ES V6 manual, that keeps overheating while driving and idle.  If I am able to pick up some speed, it cools down some but still goes up and down. If you're driving with the a/c on it overheats as well and the air becomes hot air.  Do you know what could be causing this problem?  Thanks.

Answer
Nicol,
This sounds like you may have a stuck thermostat, faulty radiator cap, weak water pump, blocked radiator, or even a malfunctioning engine coolant temperature sensor.  Even a low level of coolant can cause this.  I would recommend having a mechanic inspect this problem ASAP.  If your car is allowed to overheat, it can warp the head gasket.  And replacing that can be several hundreds of dollars in parts and labor, when your problem may only be a $3 radiator cap.
Good luck!