What are the symptoms of a faulty thermostat?
2 Answers
The symptoms of a faulty thermostat are: 1. Coolant leakage, with an abnormal drop in coolant level; 2. Engine overheating. After the engine reaches normal operating temperature, if there is a significant temperature difference between the upper and lower radiator hoses, it indicates that the thermostat may not be opening properly; 3. Slow engine warm-up. In this case, check if the thermostat is stuck in the open position, allowing full coolant circulation. The thermostat is a valve that controls the flow path of the coolant, functioning as an automatic temperature-regulating device. It typically contains a temperature-sensitive component that expands or contracts to open or close the flow of air, gas, or liquid. The purpose of the thermostat is to prevent the engine from becoming too cold. For example, after the engine reaches normal operating conditions, in winter driving conditions, without a thermostat, the engine temperature might remain too low.
I've repaired many cars, and the symptoms of a faulty thermostat are quite obvious: the most common is engine overheating—the dashboard temperature gauge spikes into the red zone, steam billows from the front of the car, and in severe cases, you can smell burning from the undercarriage. Alternatively, the engine remains ice-cold, warming up as slowly as a snail in winter, with a sharp increase in fuel consumption and reduced power. The heater also suffers, blowing cold air no matter the setting. During inspection, you can feel the temperature difference between the upper and lower radiator hoses—if stuck in the closed position, one hose will be hot while the other remains cold. If not repaired promptly, engine overheating can ruin the cylinder head, while excessive cold increases internal wear and shortens lifespan, making repairs far costlier than replacing the thermostat. Before long trips, it's wise to monitor the temperature gauge to prevent major issues.
