Coolant Temperature Light: Engine Overheating Guide
Written by Muneeb Rana · Last updated 21 October 2026
Quick answer: A red coolant temperature light means the engine is overheating or the coolant level is low. Pull over safely, switch off and let the engine cool. Never open a hot radiator or coolant cap. A blue version of the light on some cars only means the engine is still cold, and it goes out as the car warms up.
TL;DR
- Colour: Red (some cars show blue when the engine is cold).
- Red: stop as soon as it's safe and let the engine cool.
- Fix the cause rather than just clearing the light, and log the repair.
The coolant temperature light is one of the dashboard warnings drivers search for most. This guide covers what it looks like, what it means, how urgent it is and what to do, in plain English. Your owner's manual has the exact symbol and advice for your car.
What does the coolant temperature light look like?
| Symbol | A thermometer floating in waves |
| Colour | Red (some cars show blue when the engine is cold) |
| How urgent | Red: stop as soon as it's safe and let the engine cool. |
Warning lights follow a rough traffic-light code: red means a serious problem or safety issue, so stop when it's safe; amber or yellow means something needs attention soon; green or blue is information only. See the full dashboard warning lights guide for every common symbol.
What the coolant temperature light means
The AA notes that some cars use a blue temperature symbol for a cold engine. That one is information, not a warning.
Common causes:
- Low coolant from a leak
- A failed thermostat
- A failing water pump
- A broken cooling fan or fan relay
- A blocked radiator
- A head gasket problem (often with white exhaust smoke)
What to do when the coolant temperature light comes on
- Switch off the air conditioning; turning the heater to full can draw some heat away while you find a place to stop.
- Pull over and switch off the engine.
- Wait until the engine is fully cool before opening anything.
- Check the coolant reservoir level and top up with the correct coolant if low.
- If it overheats again, get it inspected; don't keep driving.
Can you drive with the coolant temperature light on?
No, not while it's red. Driving an overheating engine can warp the cylinder head or blow the head gasket.
If you're not sure, treat it as the more serious case. A tow costs far less than a ruined engine, gearbox or set of brakes. If several warning lights come on at once, that often points to an electrical or charging problem; see the check engine light guide and the battery light page.
How to reset or clear it
Don't just clear the light. Most warning lights go out on their own once the fault is fixed, sometimes after a few drive cycles. Clearing a code with a scanner without fixing the cause only hides the problem until it returns, and it can make an emissions test fail because the car's readiness monitors reset.
Keep a record of warning lights and repairs
Write down the date, odometer reading, what the light looked like, the fault code if you had it read, and what fixed it. If the same light comes back, that history saves diagnosis time and money. In CarO you can log the repair and its cost in the car repair log, and set a follow-up with the service reminder tool. For a routine check that catches problems before a light comes on, use our car maintenance checklist. Related: coolant flush guide and seasonal maintenance guide.
Download CarO free on the App Store or Google Play. Free with ads; optional in-app purchases.
Sources
- The AA: Dashboard warning lights and what they mean: www.theaa.com (accessed 21 October 2026)
- Consumer Reports: What the Dashboard Warning Lights Mean in Your Car: www.consumerreports.org (accessed 21 October 2026)
- AAA: Car Fluids, How to Check and Maintain Them: www.aaa.com (accessed 21 October 2026)
Disclaimer: CarO and this website give general car-care information, not professional advice. Maintenance intervals and specifications vary by vehicle, so always follow your owner's manual and a qualified mechanic. Mileage and cost figures are estimates; check local tax rules before using any log for deductions.
FAQ
What does the coolant temperature light mean?
A red coolant temperature light means the engine is overheating or the coolant level is low.
Is it safe to drive with the coolant temperature light on?
No, not while it's red. Driving an overheating engine can warp the cylinder head or blow the head gasket.
What colour is the coolant temperature light?
Red (some cars show blue when the engine is cold). Red warnings mean stop when safe, amber means get it checked soon, and green or blue lights are information only.
How do I turn off the coolant temperature light?
Fix the underlying cause; the light usually goes out by itself, sometimes after a few drive cycles. Clearing the code without a repair only hides the problem.
How much does it cost to fix the coolant temperature light?
It depends entirely on the cause, from nothing for a loose cap or released parking brake to a major repair. Get the fault diagnosed and ask for an itemized estimate before approving work.
Track this in CarO
CarO is a free car maintenance tracker app for iPhone and Android that keeps a full service history, reminds you about oil changes and inspections by mileage or date, and logs fuel fill-ups with MPG, odometer readings and car expenses for every vehicle you own. Logs are stored in the cloud and can be exported as CSV.
