How to Determine if the Thermostat is Faulty?
2 Answers
Methods to determine if the thermostat is faulty: 1. After starting the engine, open the filler cap of the cooling water tank. If there is no water flow observed inside the cooling water tank, it indicates that the thermostat is damaged or there is debris stuck in the main valve switch; 2. Start the engine and feel the upper and lower water pipes after a few minutes. If the temperatures of the upper and lower water pipes remain consistent, it indicates a thermostat malfunction; 3. Use an infrared thermometer to target the thermostat housing and measure the temperature changes at the inlet and outlet of the thermostat. When the engine starts, the temperature at the inlet should increase. If there is no temperature change, it means the thermostat is not functioning properly and needs replacement.
As an experienced driver, I can tell problems from the coolant temperature gauge. After normal driving, the temperature stabilizes in the middle position; if the temperature keeps failing to rise and stays in the low-temperature zone, it may indicate that the thermostat is stuck in the open position, preventing the engine from warming up properly. Conversely, if the temperature soars into the red zone with the warning light on, the thermostat might be stuck closed, causing insufficient cooling. For a quick check, try turning on the heater: if it blows cold air instead of warm air, this also confirms a thermostat malfunction. This issue shouldn't be ignored—I've encountered it several times where the heater didn't work in winter, and it turned out to be a faulty thermostat. After repair, everything returned to normal. Long-term neglect can lead to increased engine wear, higher fuel consumption, and elevated maintenance costs. So, if you suspect an issue, take it to a mechanic for inspection to avoid endless trouble later.
