While the engine runs
Car overheats in traffic and cools down when moving: what is wrong
If the temperature rises while you are stopped or in traffic and drops again once you move, the radiator is not being cooled without the airflow from driving. Usually the electric fan does not switch on, the radiator is clogged or the coolant is low.
See a garage soonWhile the engine runs
Reviewed by Daniel Morales, founder of Reprorace SL, on
Is it serious? Can I keep driving?
Carefully, and only as far as the garage. You can drive while watching the gauge, but see a shop soon. If the needle reaches the red zone or the temperature light comes on, stop as soon as it is safe and switch the engine off: carrying on can damage the head gasket.
A careful, general answer: only someone who inspects the car can say whether it is safe to drive. When in doubt, stop somewhere safe and call for assistance.
Most likely causes
- Electric fan not switching on: because of the fan motor, a relay, a fuse or its control module.
- Temperature sensor: if it reads wrong, the control unit does not start the fan in time.
- Radiator clogged on the outside: leaves, bugs or dirt between the fins.
- Low coolant: with less fluid, the engine heats up sooner.
- Thermostat or water pump: less likely if the temperature is normal on the move.
Listed from more to less common in general; on your car they may be different. A fault-code reading and a check at the garage confirm which one it is.
To understand it better: What does the engine thermostat do and what does P0128 mean? What is live data and what is it for?
Car system: Cooling
What you can check yourself
With the engine hot and the car stopped, listen for the fan switching on as the needle rises.
Turn on the A/C: on many cars the fan should start right away.
With the engine cold, check the coolant level.
Look at the front of the radiator through the grille in case it is blocked.
Safe checks only: with the engine off and cold whenever you look under the hood, without taking anything apart and without touching hot or moving parts.
Related fault codes
- P0480Fan 1, control circuit: malfunction
- P0483Fan rationality check: malfunction
- P0217Engine coolant: over temperature
- P0128Coolant thermostat: coolant temperature below the thermostat regulating temperature
- P2181Cooling system: performance
Generic codes that often come with this symptom. Seeing one does not confirm the cause: it is where the diagnosis starts.
How the ECO-LITE helps diagnose it
Plugged into the OBD socket, the ECO-LITE reads the fault codes of the control units that answer, with the freeze-frame data captured when the fault happened, and shows live data on your phone or computer. With your permission, your garage can see them remotely before you bring the car in.
What to look at here: live coolant temperature, fan status if the car reports it and fan or temperature codes.
Frequently asked questions
Can I turn on the heater to cool the engine?
Yes, as an emergency measure: the heater draws some heat away from the engine. It is not a repair.
Why does it not overheat on the highway?
Because the airflow from driving goes through the radiator. When stopped, only the fan moves that air.
Which codes does it usually set?
P0480 and the codes after it (fan circuit) or P0217 (overheating), depending on the car.
Keep reading
- Engine cooling: how it works and what fails
- Engine temperature warning light on: what to do
- Engine cooling fan will not stop: when it is normal and when not
- Low coolant warning light on: what to do
- Car symptoms: what they mean and what to do
- Check engine light on: what to do
- How to read and clear your car's fault codes
- OBD fault codes: what each one means