What does the coolant light mean?
What It Means
The coolant light (often a thermometer symbol) indicates that the engine temperature is too high or that the coolant level is low. Driving with an overheated engine can cause warped heads, blown head gaskets, and permanent engine damage.
Common causes include low coolant due to a leak, a faulty thermostat, a failing water pump, a broken radiator fan, or a clogged radiator. In some cars, the light may also indicate a sensor issue.
- Low coolant level (leak)
- Faulty thermostat
- Failing water pump
- Broken radiator fan
- Clogged radiator
- Bad coolant temperature sensor
What to Do
If the coolant light comes on, pull over safely and turn off the engine. Do not open the radiator cap or coolant reservoir while the engine is hot; pressurized steam can cause severe burns. Wait at least 30 minutes for the engine to cool.
Once cool, check the coolant level in the reservoir. If it's low, add a 50/50 mix of coolant and water (or premixed coolant). If the light remains on or the coolant is boiling, have the car towed to a mechanic. Do not continue driving.
- Pull over and shut off the engine
- Wait for the engine to cool completely
- Check coolant level and top off if needed
- If light persists, do not drive; call for a tow
- Never remove the radiator cap while hot
Common mistakes
- Opening the radiator cap while the engine is hot, risking severe burns.
- Driving with the coolant light on, which can quickly lead to engine failure.
- Adding cold water to an overheated engine, which can crack the block.
