Warning lights

Engine temperature warning light on: what to do

The red temperature warning light (a thermometer over waves) warns that the coolant is too hot. Driving on can warp the cylinder head or damage the head gasket: stop as soon as it is safe, switch off the engine and let it cool down.

Stop as soon as it is safeWarning lights

Updated on October 13, 2026

Reviewed by Daniel Morales, founder of Reprorace SL, on October 13, 2026

Is it serious? Can I keep driving?

Do not keep driving. Stop and switch off the engine. Do not open the coolant cap while it is hot: the system is under pressure and can scald you. If coolant is missing once it has cooled and there is no obvious leak, still have it checked before trusting the car again.

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

Low coolant: from a leak in a hose, the radiator, the water pump or the heater matrix.
Radiator fan: if it does not start in traffic or at idle, the temperature climbs while the car stands still.
Thermostat stuck closed: coolant does not reach the radiator even with the right level.
Water pump or its belt: a worn pump or a broken belt stops the circulation.
Head gasket: pushes gases into the system and expels coolant; it often comes with white smoke and a falling level.

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

Wait until the engine has cooled completely before opening the hood and looking at the reservoir.
Check that the level sits between the minimum and maximum marks of the expansion tank.
Look for puddles under the car or dried coolant (usually colored) on hoses and the radiator.
If you top up, use the coolant in the handbook; plain water is only an emergency measure.

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

P0217Engine coolant: over temperature
P0118Engine coolant temperature sensor 1, circuit: signal high
P0117Engine coolant temperature sensor 1, circuit: signal low
P0115Engine coolant temperature sensor 1, circuit: malfunction
P0480Fan 1, control circuit: malfunction
P0128Coolant thermostat: coolant temperature below the thermostat regulating temperature

Generic codes that often come with this symptom. Seeing one does not confirm the cause: it is where the diagnosis starts.

All fault codes

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, intake air temperature, engine speed and, depending on the car, the fan command.

See the ECO-LITE See it in the shop

Frequently asked questions

What does the blue temperature light mean?

That the engine is still cold. It is for information only: drive gently until it goes out.

Can I turn the heater on to bring the temperature down?

Heater at full heat and full fan help to shed heat while you find somewhere to stop, but they do not replace switching off the engine.

I topped it up and the light no longer comes on. Problem solved?

Not necessarily: coolant does not get used up by itself. If it was low, there is a leak or an internal loss that the garage needs to find.

Does the fault code help?

Yes: P0217 means overheating, P0128 a thermostat that does not let the engine warm up and P0115 to P0118 a sensor fault, which can also give false readings.