The coolant temperature warning light (usually a thermometer symbol in red, or a temperature gauge reading H) means your engine coolant is overheating. This is a situation that requires you to act quickly and correctly to avoid serious and costly engine damage.
What causes engine overheating
- Low coolant level: The most common cause. A leak in the cooling system or a faulty radiator cap can allow coolant to escape over time.
- Failed thermostat: The thermostat regulates coolant flow. If it sticks closed, coolant cannot circulate to the radiator for cooling.
- Radiator blockage: Debris or scale buildup inside the radiator reduces cooling efficiency.
- Failed water pump: The pump circulates coolant around the engine. If it fails, coolant stops moving.
- Head gasket failure: Combustion gases leaking into the cooling system cause rapid overheating and loss of coolant.
What to do if the warning light comes on
Turn off the air conditioning (which puts extra load on the engine). Turn the heater to maximum heat and full fan speed. This sounds counterintuitive but it helps draw heat away from the engine. If the temperature does not drop within a minute or two, pull over and stop the engine.
Do not open the bonnet immediately. Wait at least 15 minutes for the engine to cool before checking anything. Never open the coolant reservoir cap on a hot engine. Pressurised scalding coolant will spray out.
Can you top up coolant yourself
Only when the engine is completely cold. Use the correct coolant type for your vehicle (check the handbook) mixed with water to the correct ratio, or use pre-mixed coolant. Do not use plain water as an ongoing solution.
If your temperature light has come on or you suspect a cooling system problem, call Steins Garage on 0131 554 3423 before driving further.