Thermostat, also known as thermostat, is used to automatically adjust the amount of water entering the radiator according to the temperature of the cooling water, change the water circulation range, to adjust the cooling capacity of the cooling system, and ensure that the forklift engine works within the appropriate temperature range. The thermostat must be kept in good technical condition, otherwise it will seriously affect the normal operation of the engine. If the main valve of the thermostat is opened too late, the engine will overheat; If the main valve is opened too early, the engine warm-up time will be prolonged and the forklift engine temperature will be too low. At this time, it can be judged whether the thermostat is in good working condition. When the engine starts to run cold, if there is still cooling water flowing out of the water inlet pipe of the upper water chamber of the water tank, it means that the main valve of the thermostat cannot be closed; When the engine cooling water temperature exceeds 70 ℃, there is no cooling water flowing out of the water inlet pipe of the upper water chamber of the water tank, which means that the main valve of the thermostat cannot be opened normally. At this time, it needs to be repaired.