The judgment method of thermostat is:
1. Check after starting the engine. Open the filler cap of the cooling water tank and check whether there is water flow in the cooling water tank. If there is no water flow, it means that the thermostat is damaged or something is stuck between the main valve switches.
You can judge by feeling the temperature of the upper and lower pipes with your hands. Start the engine first, and touch the upper and lower pipes after 3 minutes. If it is a good thermostat, the temperature of the upper tube and the lower tube is different. Generally, the upper tube is hot and the lower tube is cold. When the engine water temperature reaches 90℃, the upper and lower pipes are hot, which proves that the thermostat is good. If the temperature of the upper and lower pipes is always the same after starting the engine, it means that the thermostat is broken;
3. Dismantle the thermostat from the car to do hot and cold water experiments, and observe whether the thermostat will open with the increase of water temperature and whether there is card sticking.