Generally speaking, the type of hydraulic oil to be used is selected based on two conditions; the climate of the location where the equipment will be used, and the design of the various devices in the hydraulic system.

Note that sometimes the synthetic materials used in the packing seals, etc. will chemically react with the hydraulic oil, so always use the recommended brand names.

* The ISO viscosity grade indicates the kinematic viscosity at 40°C.

For example, hydraulic  oil VG46 has a kinematic viscosity of 46 cst (centistokes) at 40°C (oil temperature).

These are many quality requirements for hydraulic for hydraulic oil, but the most important of these is that the oil has an appropriate viscosity not changing much with changes in temperature.

International friction is increased, heat is generated, and energy loss is great.

Resistance within the circuit increases, and pressure loss increases.

Leakage within the pump increases, volume efficiency is diminished, and the required pressure cannot be achieved.

Due to internal leakage in the control valve actuator, the cylinder is retracted by the load, and the motor cannot produce the required output.