Thermostat, also known as temperature regulator, is used to automatically adjust the amount of water entering the radiator according to the temperature of the cooling water, change the circulation range of the water, adjust the heat dissipation capacity of the cooling system, and ensure that the forklift engine operates within the appropriate temperature range. The thermostat must be maintained 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, it will cause the engine to overheat; If the main valve is opened too early, it will prolong the engine preheating time and cause the engine temperature to be too low. At this point, it can be determined whether the working condition of the thermostat is good. When the engine starts cold running, if there is still cooling water flowing out from the inlet pipe of the upper water chamber of the water tank, it indicates that the main valve of the thermostat cannot be closed; When the temperature of the engine cooling water exceeds 70 degrees Celsius and there is no cooling water flowing out from the inlet pipe of the upper chamber of the water tank, it indicates that the main valve of the thermostat cannot be opened normally, and repair is needed at this time.