* Faulty Coolant Temperature Sensor (CTS): This sensor tells the car's computer the engine's temperature. A faulty sensor might be sending a false reading, triggering the light even if the engine is not overheating. This is a very common cause.
* Low Coolant Level (despite seeming full): While you've checked the radiator, the coolant reservoir might be low. Also, there might be an undetected leak somewhere in the system (hoses, radiator, water pump, etc.) that's slowly depleting the coolant, even though the radiator appears full at the moment.
* Head Gasket Leak: A blown or leaking head gasket can allow coolant to mix with engine oil or enter the combustion chamber. This often leads to overheating and pressure build-up in the cooling system, triggering the light even if the radiator is currently full. Often you'll notice milky oil (oil mixed with coolant) or white smoke from the exhaust in this case.
* Faulty Coolant Level Sensor: Some vehicles have a sensor specifically to monitor the coolant level in the reservoir tank. A faulty sensor could trigger the light regardless of the actual level.
* Wiring Problem: A short circuit or broken wire in the coolant system's electrical components could cause the light to illuminate erroneously.
* Faulty Gauge or Light Bulb: While less likely, it's possible there's a problem with the light itself or the instrument cluster.
What to do:
1. Check the coolant reservoir: Make absolutely sure the coolant reservoir is full and at the correct level, not just the radiator.
2. Inspect for leaks: Carefully examine all hoses, clamps, the radiator itself, and the water pump for any signs of leaks. Look for wet spots, stains, or puddles under the car.
3. Check the engine oil: Look for milky or foamy oil, a sure sign of coolant mixing with oil (indicating a possible head gasket problem).
4. Check for overheating symptoms: Does the engine overheat? Is the engine temperature gauge showing high readings?
If you've checked all these and the light remains on, you'll likely need to take your Malibu to a mechanic for diagnosis. They have the tools and expertise to pinpoint the problem accurately and safely. Driving with an overheating engine can cause significant damage. Don't ignore the light.
