The most common causes of overheating are a low coolant level from a leak, a failed thermostat, a weak water pump, a cooling fan that is not running properly, a blocked radiator or, in the worst case, a failed head gasket. If the temperature gauge climbs into the red, pull over and switch off; driving on can destroy the engine.
Stand-in photoWhat to do right now
- Turn the AC off and the heater on full; it pulls heat from the engine.
- If the gauge keeps rising, pull over safely and switch off.
- Do not open the coolant cap while hot; the system is pressurised and will scald.
- Let it cool for at least 30 minutes before checking the coolant level.
- If the level is low, top up with coolant (water in an emergency) and drive gently to a workshop. If it overheats again quickly, stop and call for recovery.
The usual causes
- Coolant leak: hoses, radiator, expansion tank, water pump, heater core, or the plastic housings common on European engines.
- Thermostat stuck closed: the engine heats up fast on every drive.
- Water pump: worn impeller or bearing; sometimes a whine or a coolant leak from the pump.
- Cooling fan: a failed fan, fan clutch, resistor or relay shows up as overheating in traffic but not on the highway.
- Radiator: blocked internally, or the fins clogged with road dirt and debris.
- Air in the system after a poor repair or top-up.
- Head gasket: overheating plus white smoke, coolant loss with no visible leak, or milky oil.
Jamaican conditions
Our ambient temperatures, hills and traffic mean a cooling system with any weakness will show it. Plastic cooling-system parts on European cars become brittle after years of heat cycling. A small leak or a slightly-high gauge is the time to have the system pressure-tested, before it becomes a roadside event.
Questions
Why does it only overheat in traffic?
At speed, air flows through the radiator on its own. In traffic, the cooling fan has to do the work. Overheating only at low speed points to the fan, its control circuit or a partly blocked radiator.
Can I keep driving if it is only slightly above normal?
A gauge that sits higher than it used to is a warning, not a normal state. Have it checked before it becomes a serious overheat.