Can I drive with the coolant temperature light on?

No. It is one of the few warnings where a few miles genuinely decides whether you need a hose or a cylinder head. Stop as soon as it is safe, switch off, and let the engine cool for at least half an hour before opening anything.

Why is my temperature light on but the gauge is normal?

Usually a failing coolant temperature sensor, or air trapped in the system sitting against the sensor so it reads a pocket of steam rather than the coolant. Either way it needs checking, because you can no longer trust the gauge to tell you when there is a real problem.

Does an overheating engine fail an MOT?

Not directly, because the MOT is a static test and does not assess how the engine copes with load. But a visible coolant leak is a recordable defect, and if the car overheats while the tester is running the emissions check, the test cannot be completed and that is a major failure.

Dashboard warning light

Coolant temperature warning light

Last updated 27 July 2026

Quick answer

The engine is running hotter than it is designed to. This is one of the few dashboard warnings that can destroy an engine in the time it takes to finish a journey, so it means stopping rather than pressing on.

What to do: Stop as soon as it is safe
Can you drive?: No

Why it is red

Reserved for hazards and for faults where continuing could injure somebody or destroy something expensive. Most red lamps mean stop, though a few mean the opposite, so read the lamp rather than the colour.

What turns it on

A sensor in the coolant circuit reports temperature to the engine control unit. The lamp lights when that reading passes the safe threshold, which usually means coolant has been lost, is not circulating, or is not being cooled by the radiator.

What to do about it

Stop as soon as it is safe and switch the engine off. Continuing is what turns a split hose into a warped cylinder head, and the second of those is a different order of repair entirely.
Turn the heater to full hot and the fan to maximum before you stop if you are still moving. It pulls heat out of the engine and can buy you the distance to somewhere safe.
Wait at least half an hour before opening anything. A hot cooling system is pressurised and will scald.
Check the coolant level once cool, and look underneath for a puddle and around the engine for white or pink staining that marks a leak.
Topping up with water gets you home if the loss is small, but a system that empties again in a few miles needs recovery, not a top-up.

Can you keep driving?

Of all the lamps on this list, this is the one where carrying on costs the most. Overheating warps heads and cracks blocks, and the repair bill moves from tens of pounds to thousands in the space of a few miles. Stop, let it cool, and get it looked at or recovered.

What causes it

A coolant leak from a hose, the radiator, the water pump or the header tank
A failed thermostat stuck closed, so coolant never reaches the radiator
A radiator cooling fan that has stopped working, which shows up in traffic rather than at speed
A failing water pump, often with a whine or a weep from the pulley
A head gasket leak pushing combustion pressure into the coolant
Air trapped in the system after a botched coolant change

Does it fail an MOT?

Not on its own — but what causes it often does.

There is no MOT defect for the temperature lamp itself, and the MOT does not road test the car or check the cooling system's performance. What the tester can record is what they can see: a coolant leak is a defect under fluid leaks, and a car that overheats during the emissions test will not complete it, which is a major failure in its own right.

Fault codes that turn this light on

The lamp tells you which system reported a problem. The code stored behind it names the check that failed, which is the difference between knowing something is wrong and knowing where to look. These are the ones that commonly sit behind this symbol.

P0128 Engine not reaching normal running temperature
P0217Engine Coolant Over Temperature Condition
P0480Cooling Fan 1 Control Circuit
P0118 Coolant temperature sensor reading impossibly cold

Got a different code? Look it up — the index covers every standard OBD-II code.

Common questions

Can I drive with the coolant temperature light on?: No. It is one of the few warnings where a few miles genuinely decides whether you need a hose or a cylinder head. Stop as soon as it is safe, switch off, and let the engine cool for at least half an hour before opening anything.
Why is my temperature light on but the gauge is normal?: Usually a failing coolant temperature sensor, or air trapped in the system sitting against the sensor so it reads a pocket of steam rather than the coolant. Either way it needs checking, because you can no longer trust the gauge to tell you when there is a real problem.
Does an overheating engine fail an MOT?: Not directly, because the MOT is a static test and does not assess how the engine copes with load. But a visible coolant leak is a recordable defect, and if the car overheats while the tester is running the emissions check, the test cannot be completed and that is a major failure.

This is general guidance, not a diagnosis. Manufacturers draw the same system differently and reuse symbols for more than one function, so check the handbook for your own car before acting on anything here.

Check what your car has actually failed on

Free MOT history for any UK registration, straight from DVSA records.