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The red temperature light indicates the engine is overheating: pull over safely, let the engine idle for a few moments and then switch it off. Pressing on means risking the head gasket or a warped cylinder head, with very high costs.

What it means

The coolant has exceeded the safe temperature. Some cars show a yellow light or the needle past the middle first, then the red one.

Most common causes

• Low coolant level due to a leak from hoses, radiator or pump
• Thermostat stuck closed
• Water pump or the belt that drives it
• Cooling fan not starting (relay, resistor, sensor)
• Radiator blocked externally or internally
• Failed head gasket (bubbles in the expansion tank, rising coolant)

What to do right away

• Switch off the air conditioning and turn the heating to maximum: it helps dissipate heat
• Stop and do not open the expansion tank cap while hot: risk of serious burns
• Check the level only with the engine cold
• If the car is losing coolant, do not top up and drive off: the cause must be found

How MasterTuning helps

We read the ECU with professional tools, interpret the real fault codes and tell you what really needs repairing, without unnecessary replacements. Diagnosis, repair and software recalibration at our centres throughout Italy.

Read more: vehicle database · find an installer · what is ECU remapping

Is a warning light on? Contact us for a diagnosis or find your nearest MasterTuning centre.

Frequently asked questions

Can I drive with the temperature light on?

No: overheating damages the head gasket and cylinder head within minutes. Stop and let the engine cool down.

Can I top up with water?

Only in an emergency and to reach the workshop. The correct coolant contains anti-corrosion and antifreeze additives: it should be restored as soon as possible.

Why does the fan not start?

The typical causes are the relay, the fan resistor, the temperature sensor or the fan motor itself: a diagnosis tells them apart in minutes.