The volume of the plastic tank is too small, the heat dissipation area is not enough, and the assembly is cooled but its capacity is too small. The temperature of the gas and working environment is high, causing the oil temperature to rise. The viscosity of the oil is selected improperly, the viscosity is large, the viscous resistance is large, and the viscosity is too small, the leakage is increased, and both cases can cause the heat rise. The plastic barrel system is too long and too long, too much bending, partial pressure loss and large pressure loss along the path. Insufficient component accuracy and poor device quality, and large mechanical friction loss between activities. The fitting clearance of the fittings is too small, or the wear is caused to cause excessive clearance, and the amount of leakage inside and outside is large, resulting in a large volume loss, such as a decrease in the volume of the pump and a rapid rise in temperature. The plastic bucket selects the pumping capacity of the oil pump capacity according to the fast-forward speed. At the time of operation, most of the excess flow will overflow from the overflow valve under high pressure and generate heat. In the system, the unloading circuit is faulty or because the unloading circuit is not set, the oil pump can not be unloaded when the work is stopped, and the full flow of the pump overflows under high pressure, causing overflow loss and heating, resulting in temperature rise.