The hydraulic systems of automobiles and construction machinery use hydraulic oil as the working medium. The flow rate of the oil in this type of hydraulic system is low and the pressure is high, so it is called hydrostatic transmission. The quality of hydraulic oil will greatly affect the reliability and service life of the hydraulic system. Generally, the quality requirements for hydraulic oil are as follows:

1) Appropriate viscosity and good viscosity-temperature performance to ensure accurate and sensitive power transmission under the condition of changing working temperature, and to ensure the normal lubrication of hydraulic components.

2) It has good rust resistance and oxidation stability, and is not easy to oxidize and deteriorate under high temperature and high pressure conditions, and has a long service life.

3) It has good anti-foaming properties, so that the foam produced by the oil is easy to disappear under the working condition of continuous mechanical stirring, so that the power transmission is stable and the accelerated oxidation of the hydraulic oil is avoided.