Coolant temperature warning light: overheating explained
A red thermometer symbol means the engine is overheating. Continued driving risks a warped head, failed head gasket or a seized engine.
Stop or act now — a safety or mechanical risk
Immediate. Pull over as soon as it is safe and let the engine cool before touching anything.
No. Even a short distance while overheating can cause damage that costs more than the vehicle is worth.
Common causes
- Coolant loss through a leaking hose, radiator, water pump or expansion tank
- Failed thermostat stuck closed
- Radiator cooling fan or its relay not running
- Blocked radiator core or a badly contaminated air path
- Head gasket failure pressurising the cooling system
What to do next
- 1Stop safely, switch off, and open the bonnet only once the engine has cooled.
- 2Never open the expansion tank or radiator cap while hot — scalding coolant is released under pressure.
- 3Once cool, check the coolant level and look for obvious leaks or steam trails.
- 4Check whether the cooling fan runs when the engine is hot and the ignition is on.
- 5Recover the vehicle rather than driving it if the level keeps dropping.
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Ask the AI mechanicFrequently asked
- Can I top up with plain water?
- In an emergency, water gets you to safety, but it lowers the boiling point and removes corrosion protection. Have the system drained and refilled with the correct coolant mix afterwards.
- What does a blue temperature light mean?
- Blue is the opposite: the engine is still below operating temperature. It is not a fault, and it goes out as the engine warms up.
General guidance only. Symbols and thresholds vary between manufacturers — always confirm against your vehicle's owner manual, and treat any red lamp as a reason to stop.
Other dashboard lights
- Check engineThe check engine light (an engine-block outline, usually amber) means the engine management system has stored a fault code. Steady means investigate soon; flashing means stop driving.
- Oil pressureThe red oil-can symbol means the engine has lost oil pressure. This is the most serious light on the dashboard — continued driving can destroy the engine in under a minute.
- ABSThe amber ABS lamp means the anti-lock braking system has disabled itself. Normal braking still works, but the wheels can lock under hard or emergency braking.
- Brake systemThe red brake light (an exclamation mark inside a circle) covers three very different things: the parking brake being applied, low brake fluid, or a hydraulic circuit fault.
- Battery / chargingThe red battery symbol means the charging system is no longer supplying enough voltage. The car is running on stored battery charge and will eventually stop.
- Tyre pressure (TPMS)The amber horseshoe with an exclamation mark means at least one tyre is significantly below its target pressure — or the monitoring system itself has a fault.
- Airbag / SRSThe SRS or airbag symbol means the supplementary restraint system has detected a fault and has disabled itself. In a crash, the airbags or pretensioners may not fire.
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