To troubleshoot an overheating car, check the coolant level, look under the hood to see if the electric fan is running, examine the radiator fan switch and check to see if the thermostat is opening properly. Overheating may also be caused by a broken fan belt or clogged radiator.
A low coolant level is the most common reason for an overheating vehicle, so add more coolant fluid if necessary. If that doesn't work, allow the car to idle long enough for the engine to become hot, and then when the temperature gauge has climbed significantly, check under the hood to see if the fan has activated. If not, the overheating is caused by a problem with the fan.
To see if the electric fan's motor is broken, disconnect the wiring harness from the radiator fan switch and inset a jumper wire into both contacts. If the fan does not turn on, it is burnt out. If the vehicle uses a fan belt, inspect it to see if it is broken.
If the vehicle overheats most frequently when traveling at highway speeds, the problem may be that the thermostat is not opening properly. Old coolant buildup can clog the radiator, causing the vehicle to overheat. Flush the radiator annually to prevent this. It is also important to check the oil regularly to keep the engine lubricated.