Temperature warning light and engine overheating: what to do, causes and affected cars

The temperature warning light (a thermometer above waves) signals real overheating, a lack of coolant or a faulty sensor. When in doubt, the rule is the same: stop the car to avoid damaging the engine (Caradisiac).

What to do if the engine overheats

If the red light comes on or white smoke comes from the bonnet (Caradisiac):

1. Stop straight away and switch off the engine.
2. Let it cool for 30 minutes to an hour, without opening the radiator cap or the expansion tank.
3. Then check the coolant level and look for a leak.
4. If it overheats again, do not push on: call your breakdown service.

The most common causes

A coolant leak

A loss of coolant must be dealt with quickly to avoid overheating, the engine going into protection mode and head gasket damage (Fiches-auto, Audi A4). On the Audi A6 3.0 TDI, split hoses appear from 80,000 to 120,000 km and were the subject of a recall campaign in 2022 (CarVerif). See coolant leaks.

The water pump

The water pump housing can crack and leak coolant until the engine overheats if it is not caught in time (GetCarwise, Audi TT). An Audi A1 owner reports overheating caused by a failed water pump at 45,000 km (Fiches-auto).

The cylinder head or head gasket

On the Audi A4 B7 2.0 TDI, porous cylinder heads cause overheating and coolant loss on 2004 to 2008 models (CarVerif). Persistent white smoke also points to the head gasket: see white smoke.

Regulation and sensors

A faulty coolant control valve can disturb the engine temperature (Fiches-auto, Audi A4), and a temperature sensor fooled by the heat can send wrong readings (Caradisiac). A warning light must still always be taken seriously.

Before buying a used car

Check the expansion tank level with the engine cold, look for coolant traces under the car and watch the temperature gauge during the test drive. Falling coolant, bubbles or white smoke are reasons to walk away (CarVerif, Ford Fiesta).