When Your Car Is Overheating, but It’s Not the Radiator

When your car is overheating, a busted radiator is a very common culprit, but it's not the only part under the hood that may need some attention. In some cases, the car's radiator can actually be in good repair, but other parts of the vehicle's cooling system may have failed and need replacing. Note a few of those parts here so you know where to begin looking when your car is overheating but you know the radiator is functioning properly.


Your car's engine has a thermostat, just like your heating and cooling appliances at home; the thermostat reads the temperature in the engine and the cooling system adjusts the amount of coolant that is delivered to the engine compartment accordingly. If the thermostat is broken, the valve that opens in the cooling system and which allows coolant to flow to the engine won't engage, and the engine then overheats. A broken thermostat is actually quite a common cause for an engine to overheat, so check it first.

Water pump

The water pump does just as the name implies; it pumps water around the engine to help keep it cool. When the pump dies, the engine overheats even if the radiator is in good repair. You can check the car's owner's manual to note the expected lifespan of the water pump and have it replaced as that time approaches to reduce the risk of it breaking down while you're on the road.

Air in the cooling system

The cooling system works by circulating fluids around the engine in order to keep it cool. If air gets into the cooling system, this can keep those fluids from staying cool and also restrict their circulation. Air in the cooling system may be the fault of leaking or split hoses or of not properly bleeding the radiator after repairs. A mechanic can find any damaged hoses and also bleed the cooling system, removing that air.

Radiator fan

The radiator fan helps to keep the engine cool when you're idling or driving at low speeds; when the fan breaks, your car is likely to overheat when you're driving a short distance. However, a broken fan may engage when you're driving at high speeds, since the air coming through the engine compartment forces the fan blades to spin. If you notice that the car overheats at low speeds or stop-and-go traffic but then cools down when you're on the highway, have the fan checked.