Engine Temperature Warning Light

What it means

Shown as a thermometer dipped in wavy lines of liquid, usually red, this light means the engine coolant temperature has gone above the safe limit. It is normal for it to glow for a few seconds at key-on and then go out; if it comes on while driving, stop safely and switch off the engine as soon as you can.

Related lights: Oil Pressure Warning LightLow Coolant Temperature IndicatorCheck Engine LightMaster Warning Light

Symptoms5

• Red light on, or the temperature gauge near the red zone.
• Steam from under the hood or a smell of hot coolant.
• Reduced engine power, sometimes with a message asking you to stop.
• Air conditioning stops cooling on some cars to protect the engine.
• A colored puddle under the front of the car when parked.

Possible causes7

• Low coolant from a leaking hose, radiator or connection.
• Failed cooling fan, fan relay or fan fuse.
• Thermostat stuck closed.
• Radiator clogged inside or its fins blocked with dirt outside.
• Failed water pump or a broken belt that drives it.
• Faulty coolant temperature sensor or wiring giving a false warning.
• Blown head gasket (less common and more serious).

How to diagnose5

1. Stop in a safe place and switch off the engine; do not open the radiator or reservoir cap while hot, because pressurized coolant can cause burns.
2. Once the engine is fully cool, check the coolant level in the reservoir and look for leaks or puddles.
3. After topping up, run the engine and watch whether the fan switches on as the temperature rises.
4. At the workshop: pressure-test the cooling system for leaks and compare the actual engine temperature on a scan tool with the gauge.
5. Check the thermostat and water pump, and test the coolant for exhaust gases if a head gasket failure is suspected.

How to fix6

1. Top up with the recommended coolant once the engine is cool, and fix the leaking hose or connection.
2. Replace the fan fuse, relay or fan motor as the tests indicate.
3. Replace the thermostat or temperature sensor if confirmed faulty.
4. Clean or replace the radiator, and replace the water pump or belt if needed.
5. Repair the head gasket if confirmed, and check the cylinder head for warping.
6. After the repair, warm the engine to operating temperature and confirm the gauge stays steady and the light stays off.

The cost starts with a coolant top-up, a hose or a relay, and reaches the upper end for a radiator, water pump or head gasket repair after driving while overheated.

Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026

Frequently asked questions