Coolant Temperature Warning Light — Overheating

A red coolant temperature warning light or a temperature gauge in the red zone means your engine is overheating. This is one of the most serious warnings your car can give you. An overheating engine can destroy a head gasket in minutes, and a blown head gasket can write off an otherwise healthy car.

What to do immediately:

Turn the heating to maximum and the blower to full — this turns your car's heater into a secondary radiator and may buy you a few extra minutes. Turn off the air conditioning. If the temperature continues to rise, pull over and stop the engine as soon as it's safe to do so. Do not open the coolant cap while the engine is hot — it's under pressure and can cause severe burns. Wait at least 30 minutes for the engine to cool.

What causes engine overheating:

Low coolant level — check the coolant reservoir (translucent white bottle in the engine bay) once the engine is cold. If it's empty or very low, there's a leak somewhere in the system. Top up with the correct coolant (pink or blue depending on your car — check the cap or handbook) and investigate the source of the leak.

Failed thermostat — a thermostat stuck closed prevents coolant flowing to the radiator. The engine heats up rapidly with no way to shed the heat.

Cooling fan failure — at low speeds and in traffic, the electric cooling fan is essential. If it's failed, the car overheats in traffic while running fine at motorway speed (where airflow through the radiator is sufficient).

Water pump failure — the pump circulates coolant around the engine. A failed water pump means stagnant hot coolant with no circulation. You may hear a rumbling or grinding from the engine bay.

Blown head gasket — if coolant is being pushed out of the system by combustion gases, the coolant level drops and the engine overheats. Signs include white smoke from the exhaust, mayo-like brown sludge under the oil cap, or bubbling in the coolant reservoir with the engine running.

Blocked radiator — insects, road debris, or internal scale can restrict radiator airflow or coolant flow, reducing cooling capacity.

After overheating — what to check:

Once the engine is cold, check the coolant level, look underneath for puddles, check the oil for any cream-coloured contamination (head gasket sign), and look for white smoke residue around the exhaust. Do not restart until the cause is identified — driving an overheated car risks permanent engine damage.