What Causes an Engine to Overheat?
An engine running hotter than normal is one of the few dashboard warnings worth treating as urgent rather than something to deal with later, since continuing to drive on an overheating engine is what turns a repairable fault into a much bigger bill.
The most common causes
- Low coolant, often from a slow leak that's gone unnoticed rather than a sudden loss
- A failing water pump, which circulates coolant and stops doing its job effectively as it wears
- A stuck thermostat, which can trap coolant in the wrong part of the system
- A blocked radiator, whether from debris outside or scale build-up inside
- A failed radiator fan, particularly noticeable in slow traffic where airflow alone isn't enough
What to do if the gauge starts climbing
Turn the heater on full, which sounds counterintuitive but pulls heat away from the engine into the cabin. Find somewhere safe to stop as soon as reasonably possible, and switch the engine off rather than letting it idle and get hotter. Don't open the radiator cap while the engine is hot, since pressurised coolant can cause serious burns.
Why continuing to drive makes it worse
An engine that overheats briefly and is dealt with promptly is usually fine. One that's driven for miles while overheating risks warping the cylinder head, which is a far more expensive repair than whatever caused the overheating in the first place. A few extra minutes waiting for recovery is genuinely cheaper than pushing on to the next junction.
Preventing it in the first place
Checking coolant level when the engine is cold, as part of a routine monthly fluid check, catches most slow leaks before they become a roadside problem.
Check a car's MOT record for any cooling system related advisories.
Check MOT history