DIY: Moderate
Car Overheating: What to Do Right Now and What Causes It
Overheating can destroy an engine in a short time, so the first job is stopping it safely. The pattern of when it happens then points to the cause.
Stay safe first
- If the temperature gauge nears the red or a warning appears, pull over safely and shut the engine off.
- While you find a place to stop, turn the A/C off and turn the heater to full hot. It pulls heat out of the engine.
- Never open the radiator cap or coolant reservoir while the engine is hot. Pressurized coolant can cause serious burns. Wait until it has cooled completely.
- Do not keep driving an overheating car to get home. Call for a tow if it overheats again.
Low coolant level, sometimes with a sweet smell or puddles
Likely causes
- Leaking hose, radiator or water pump
- Loose clamp or failed radiator cap
- Head gasket leak (white exhaust smoke, milky oil)
What to check
- When the engine is fully cool, check the coolant level in the reservoir.
- Look for puddles under the car and for wet or crusty spots on hoses and around the radiator.
- If you keep losing coolant with no visible leak, have it pressure tested, since an internal leak needs a shop.
Overheats in traffic or at idle, fine on the highway
Likely causes
- Cooling fan not turning on
- Failed fan relay, fan motor or temperature switch
- Radiator clogged with debris or scale
What to check
- With the engine warm and the A/C on, see whether the radiator fan turns on. If it never does, the fan or its relay is the likely problem.
- Look through the front of the radiator for bugs, leaves or bent fins blocking airflow.
Overheats and the heater blows cold air
Likely causes
- Very low coolant
- Air pocket trapped in the cooling system
- Stuck-closed thermostat
What to check
- A heater that stops working while the gauge climbs usually means the coolant level is low or air is in the system.
- A stuck thermostat can cause the upper radiator hose to stay cool while the engine gets hot.
Narrow it down for your vehicle
The same symptom can have different likely causes depending on your year, make, model and engine. Describe what you are seeing and CaliperAI will help narrow down the likely causes for your vehicle.
Related guides
General information about this symptom, not a diagnosis of your specific vehicle. Safety-critical work such as brakes, fuel and airbags is best left to a qualified mechanic.