Important Properties of Hydrostatic Transmission Fluids

The properties a user should look for in hydrostatic transmission oils depend on the design of the transmission and the environment in which it is expected to operate. Important properties are: antiwear, oxidation stability, antirust, demulsibility, cavitation and air entrainment, bulk modulus (compressibility), seal conditioning, viscosity and viscosity index.

Some single graded crankcase oils can be used, but their composition is changed frequently to meet changing crank-case requirements and all of the desired properties may not be included. Desired features are available in hydraulic oils specifically designed and proven in hydrostatic transmissions. For out-of-doors service a shear stable, high VI oil with a viscosity of 200 SSU at 100 F is recommended.