If the temperature gauge goes into the red or a red coolant warning lights up, act immediately. Overheating can damage the head gasket or the cylinder head itself within minutes.
What to do right away
- Switch off the air conditioning and turn the cabin heater to full – it carries some heat away from the engine.
- If the reading doesn't drop, stop somewhere safe and switch off the engine.
- Never open a hot cooling system cap! The system is under pressure and hot coolant can cause burns. Wait at least 30–60 minutes.
- With the engine cold, check the expansion tank level and look for a leak (puddle under the car, sweet smell, steam).
Common causes
- Low coolant because of a leak (hoses, radiator, water pump, heater core).
- A thermostat stuck closed.
- The radiator fan doesn't switch on (fuse, relay, motor, sensor) – overheating mainly in town and traffic jams.
- Water pump: worn impeller or drive belt.
- A clogged radiator or one covered in insects and dirt.
- Head gasket failure: bubbles in the expansion tank, white smoke, mayonnaise-like residue in the oil, coolant loss with no visible leak.
Topping up correctly
Use the coolant type specified by the manufacturer. In an emergency you can add clean water, but correct the mixture afterwards so it doesn't freeze in winter. Don't mix different coolant types without checking compatibility.
If it keeps happening
Have a cooling system pressure test done, plus a combustion gas (CO2) test of the coolant to rule out a head gasket failure. Topping up again and again and driving on usually ends expensively.
Prevention
Check the coolant level when the engine is cold every few weeks, replace coolant at the interval in your service book, and have hoses and the water pump inspected when the timing belt is changed – on many engines the pump is driven by it.
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