If your car starts overheating while you are driving, turn off your air conditioner and turn on your heater to cool the engine off. Drive to a place where you can park the car and repair it. If the car still overheats with the heater on, pull over immediately to avoid causing irreversible damage to your car engine. Diagnosing the cause of the problem requires a basic knowledge of car engines---refer to the engine repair manual for your model car if you are not familiar with the location of the parts of the cooling system.
Check the radiator, once the engine cools, to see if it contains coolant (antifreeze). Fill the radiator with coolant if it is low. If the radiator contains coolant that looks dirty, rusty or contains chunks of debris, take your car in to a mechanic to have the radiator flushed. If the radiator is severely blocked with debris or rusted on the inside, you may need a new radiator.
If the radiator does not hold water or if it needs to be refilled frequently, check for coolant system leaks. Inspect the radiator and coolant hoses for cracks or holes. Replace the radiator if it is damaged. Replace the hoses if they are damaged.
If your car only overheats when the car is stopped and idling, the problem might be the fan. To check the fan, park your car, prop the hood open and let the car idle. If the fan does not turn on when the car temperature on the dash shows the car is running hot, you need to replace the fan.
Pull the oil dipstick out and inspect the color of the oil. If the oil is a milky whitish color, the coolant is mixing with the oil, which means you have a blown head gasket.
Remove the thermostat from the engine if all of the other parts of the cooling system are working properly. The thermostat monitors the engine's temperature. When the engine starts to get hot, the thermostat opens and allows the coolant to flow through. A broken thermostat does not open, causing the engine to overheat. To check to see if the thermostat is the cause of your engine overheating, allow the car to idle with the thermostat removed. Without a thermostat, coolant will constantly flow through the engine. If the car does not overheat with the thermostat removed, the thermostat was the cause of the overheating. Install a new thermostat to fix the overheating problem.
