Signs of overheating
The temperature gauge climbs into the red, a temperature warning light comes on, steam rises from the bonnet, or the heater suddenly blows cold air. Overheating is an emergency: beyond a certain temperature, the cylinder head warps and the head gasket fails.
Pull over as soon as it is safe to do so and switch off the engine. Never open the expansion tank or radiator cap when the engine is hot: the pressurised coolant can cause serious burns.Likely causes
- Low coolant level due to a leak: coolant hose, radiator, water pump, or connector.
- Thermostat stuck closed: coolant can no longer circulate to the radiator.
- Cooling fan failure: overheating tends to occur mainly when stationary or in traffic jams.
- Faulty water pump, often driven by the timing belt.
- Head gasket failure: combustion gases enter the cooling circuit, forcing coolant out and causing it to bubble.
What to do next?
Once the engine has cooled down, check the level in the expansion tank. If topping it up is sufficient and the temperature remains stable, have the leak traced promptly. If the temperature rises again, stop driving immediately and have the vehicle towed.
What if the engine has already overheated?
An engine that has run very hot may have a warped or cracked cylinder head. If the head gasket fails or the engine loses compression, a reconditioned engine on an exchange basis, supplied as a bare engine and warranted for up to 24 months, avoids an uncertain repair. Before fitting: it is essential to fix the root cause of the overheating (radiator, pump, thermostat), otherwise the replacement engine will suffer the same fate.
