Hydrostatic drive is what makes this possible; the ability to apply variable torque to the left or right wheel. These systems require a versatile and robust hydraulic system and thus, an equally robust hydrostatic drive fluid. Lucas Oil has just the product for these mowers. This SAE 20W-50 multi-grade viscosity oil provides excellent protection against all lubricated parts, has added detergency, dispersancy and rust protection over motor oils, that are sometimes used in this application, and will not shear thin over time.