How to Determine if the Thermostat is Faulty?
2 Answers
Here are specific methods to determine if the thermostat is damaged: 1. Observe for water flow: Open the filler cap of the coolant reservoir and check if there is any water flow inside. If not, it indicates that the thermostat is damaged or there is debris stuck between the main valve switch. 2. Check for thermostat changes: Remove the thermostat from the vehicle and boil it in water, observing whether it opens as the water temperature rises. 3. Feel the hose temperature: Start the engine and after 3 minutes, touch the upper and lower hoses. If the thermostat is functioning properly, the temperatures of the upper and lower hoses should differ, typically with the upper hose being hot and the lower hose being cool.
I've been driving a taxi for many years, and a faulty thermostat is a common issue in cars. I've encountered it several times myself. The main way to diagnose it is by observing the temperature gauge: if the engine heats up quickly but the temperature fluctuates erratically, or if the temperature takes forever to rise after a cold start, that's suspicious. Additionally, feel the upper and lower radiator hoses—if the engine is hot but one hose is cold and the other is scalding, it's likely the thermostat is stuck and not allowing coolant to circulate. If the temperature shoots up past the red line while driving, with the fan running loudly but no cooling effect, that also points to a thermostat issue. Sometimes, you might also notice the heater not blowing hot air or increased fuel consumption. Don’t delay if these signs appear—engine overheating can easily blow the head gasket, leading to costly repairs. I usually pull over immediately to check the radiator fluid level, and if it’s fine, I drive slowly to the repair shop to avoid turning a small issue into a big one. During routine maintenance, remind the mechanic to inspect it—replacing a thermostat costs just a few bucks and can easily extend the engine’s lifespan.
