Two important factors in selecting an oil are:
1. antiwear additives - The oil selected must contain the necessary additives to insure high antiwear
characteristics and excellent chemical stability;
2. viscosity - The oil selected must have proper viscosity to maintain a lubricating film at system
Industrial grade antiwear type hydraulic oils should be used. These oils contain additives specifically
designed for hydraulic systems.
New machines come from the factory with Sun 2105 (5W20) hydraulic oil.
This oil facilitates start up at temperatures down to 5°F. and is satisfactory up through normal operating
temperatures. When replenishment of hydraulic oil becomes necessary, SAE 10W oil with 0.6% zinc
dithiophosphate, which is readily available on the open market, may be used. SAE 10W with this additive
is compatible with factory installed oil. However, if 100% replenishment is necessary and a SAE 10W oil
with appropriate additives is used, start up temperature is raised to 10 F. Extremes of either hot or cold
temperatures must be considered on an individual basis. Consult factory for specific recommendations
regarding oil viscosity, special equipment, and operating procedures. Regardless of temperature and oil
viscosity, always use suitable start-up procedures to ensure adequate lubrication during system warm-up.
Oil viscosity is important because it has a direct bearing on efficient transmission of power. An oil must
flow readily through the system with a minimum of pressure and flow loss. Positive lubrication depends on
viscosity. The oil must be sufficiently light to get between the components machined surfaces and still
maintain a lubricating film at system operating temperatures. Oil too light may cause the following
conditions in the systems:
lower volumetric efficiency of the pump;
increased component wear;
loss of system pressure;
lack of positive hydraulic control;
lower overall efficiency.