An engine overheats when the cooling system cannot carry heat away fast enough. The usual causes are low coolant from a leak, a thermostat stuck closed, a failing water pump, a clogged or damaged radiator, a cooling fan that does not run, or a failed head gasket. If the temperature gauge climbs, turn off the air conditioning, turn the heater to full hot to pull heat away from the engine, and pull over and shut it off if it keeps rising.
What to do if your car is overheating
- Turn off the air conditioning and set the heater to maximum heat and fan.
- If the gauge keeps rising, pull over safely and switch off the engine.
- Do not open the radiator cap or reservoir while hot; pressurized coolant can scald.
- Once cool, check the coolant level and look for leaks, a broken belt or a fan that is not working.
- Do not keep driving an engine that is overheating; it can warp the heads and blow the head gasket.
Common causes of engine overheating
- Low coolant: from a leak in the radiator, hoses, water pump or heater core; see coolant leak.
- Thermostat stuck closed: coolant cannot reach the radiator.
- Water pump failure: a worn impeller or failed bearing stops circulation.
- Radiator problems: clogged passages, bent fins or internal corrosion reduce cooling.
- Cooling fan: a failed electric fan, relay or fan clutch, often noticed when the car overheats in traffic but is fine on the highway.
- Air in the system: after coolant service, an air pocket can cause hot spots.
- Head gasket failure: combustion gas pushes into the coolant; see signs of a blown head gasket.
- Heavy load: towing in hot weather, or added power from a supercharger, can exceed a stock cooling system.
Overheating in traffic vs on the highway
Overheating at idle or in traffic usually points to airflow: a fan, fan clutch or relay. Overheating at speed or under load points to flow and capacity: the radiator, water pump, thermostat or a head gasket.
Preventing overheating
Check the coolant level when the engine is cold, replace hoses and the cap as they age, flush and refill the coolant on the schedule in your manual, and keep the radiator fins clear of bugs and debris.
Cooling upgrades for supercharged cars
Adding boost adds heat. For the C5, C6 and C7 Corvette we carry DeWitts radiators and radiator-and-fan combos, including shortened radiators that make room for a front-mounted supercharger; see the DeWitts page, our supercharger kits by platform, and what does an intercooler do?
More guides: coolant temperature sensor · serpentine belt · seized engine · car overheating when idling · cracked engine block or warped head · losing coolant but no leak · heater blowing cold air · thermostat stuck open or closed · bad radiator symptoms.
Trouble codes: P0217 Engine Over Temperature · P0128 Thermostat Below Regulating Temp · P0118 Coolant Temp Sensor High · P0480 Cooling Fan 1 Control Circuit · P0481 Cooling Fan 2 Control Circuit · all OBD2 codes.
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