How to Check a Thermostat?
2 Answers
Thermostat inspection method: Remove the thermostat from the engine, clean it, and then heat it in hot water. Use a thermometer with a range of 100 degrees Celsius to measure the temperature. Check whether its performance is good and whether it works reliably according to the specified temperature for the thermostat valve to open or the side valve to close. The thermostat is a valve that controls the flow path of the coolant, an automatic temperature control device that usually contains a temperature-sensitive component, which opens and closes the flow of air, gas, or liquid by means of thermal expansion or contraction. The main type of thermostat used is the wax-type thermostat. When the cooling temperature is below the specified value, the refined paraffin in the temperature-sensitive body of the thermostat is in a solid state, and the thermostat valve closes the passage between the engine and the radiator under the action of the spring. The coolant returns to the engine through the water pump, performing a small circulation within the engine.
As a seasoned driver with over a decade of experience, checking the thermostat feels like catching up with an old friend. First, you need to prepare before a cold start—pop the hood, then start the engine and let it idle. Keep an eye on the coolant temperature gauge or the temperature indicator on the dashboard. A properly functioning thermostat should raise the coolant temperature to around 80°C within 5 to 10 minutes of startup. If the temperature barely moves or suddenly spikes above 90°C, the thermostat might be stuck closed. Next, feel the upper radiator hose (connected to the radiator)—it should be warm, while the lower hose should stay cool. If both are hot, the thermostat may have failed. For a more accurate test, I remove the thermostat and place it in hot water, checking if it opens automatically at around 85°C—a simple method that requires a thermometer. In short, a faulty thermostat can lead to engine overheating, damage, and even increased fuel consumption, so don’t delay repairs if issues arise. Before starting, gather tools like gloves and a basin—safety always comes first.
