Fix a car that overheats

Steps

Goal: Confirm the symptom, rule out coolant and leaks, then isolate the cause—thermostat, radiator cap, radiator, fan, water pump, or head gasket.

• Run the engine and watch the temperature gauge. If it rises into the red or the warning light comes on, the cooling system has failed.
• Good: The gauge rises into the red or warning light on—cooling fault. Proceed to Check coolant and leaks.
• Bad: The gauge stays cold—different problem. See fix-car-heater-will-not-heat.

Check coolant and leaks

Goal: Rule out low coolant and leaks before testing other components.

• Check the coolant reservoir when the engine is cold. The level should be between min and max. Add coolant per your vehicle specification if low. Do not open the radiator cap when the engine is hot—pressure can spray scalding coolant.
• Look under the car for puddles of green, orange, or pink fluid. Check around the radiator, hoses, water pump, and heater core connections.
• Good: Coolant level is correct and no leaks. Proceed to Thermostat and radiator cap.
• Bad: Low coolant or leaks found—add coolant and fix leaks, or call a mechanic for radiator or water pump leaks.

Thermostat and radiator cap

Goal: Test the radiator cap and thermostat—both can cause overheating.

• When the engine is cold, remove the radiator cap and inspect the rubber seal for cracks. Use a radiator cap pressure tester if available—the cap should hold the pressure stamped on it (typically 13–16 psi). Replace the cap if the seal is damaged or it fails the pressure test.
• Run the engine until it starts to overheat. Feel the upper radiator hose—it should get hot when the thermostat opens. If the hose stays cold while the engine overheats, the thermostat may be stuck closed.
• Good: Cap holds pressure and the upper hose gets hot when the engine warms. Proceed to Radiator, fan, and water pump.
• Bad: Cap fails the pressure test or thermostat stuck closed—replace the cap or thermostat, or call a mechanic.

Radiator, fan, and water pump

Goal: Check the radiator, cooling fan, and water pump.

• Look through the grille for leaves, bugs, or debris blocking the radiator fins. Flush debris from the front with a hose (engine off). Check that the cooling fan runs when the engine is hot—electric fans turn on when the coolant reaches a set temperature.
• Check the water pump for coolant leaking from the weep hole under the pulley. With the engine running, the pump pulley should spin. If the belt is on and the pulley does not spin, the pump has failed.
• If you see white smoke from the exhaust, milky oil on the dipstick, or bubbles in the coolant reservoir when running, suspect head gasket failure—stop driving and call a mechanic.
• Good: Radiator is clear, fan runs, water pump spins with no leak. If the car still overheats, call a mechanic.
• Bad: Radiator blocked, fan does not run, water pump failed, or head gasket suspected—call a mechanic.

When to get help

Call a mechanic if:

• The coolant keeps dropping and you cannot find the leak.
• The water pump has failed.
• The radiator is clogged or leaking.
• You suspect head gasket failure (white smoke, milky oil, bubbles in coolant).
• You are not comfortable working with coolant or engine components.

Do not drive an overheating car—it can cause severe engine damage.

Verification

• The temperature gauge stays in the normal range when the engine runs.
• The coolant level is correct and there are no leaks.
• The radiator cap holds pressure when tested.
• The upper radiator hose gets hot when the engine warms.
• The cooling fan runs when the engine is hot.
• The water pump pulley spins and there is no leak at the weep hole.