Chlorophenyl substituted silicones have better lubricating properties than lightly phenylated methyl silicones with similar physical properties. The best load-carrying and anti-wear properties are obtained with fluorosilicones at some loss in low-temperature properties. This paper describes a new class of silicone copolymers containing both trifluoropropyl and halophenyl substitution which can cover a temperature span of −100 F to 650 F. Data are included showing that this combination improves both low and heavy load anti-wear properties for steel. Physical, friction and wear, and stability data are given describing these properties as a function of the type, and amount of halogen on the phenyl as well as with varying ratios of trifluoropropyl to halophenyl substitution. Differences in lubricating performances and mechanisms for various halogenated groups are discussed to explain the improvements noted for the combination of halophenyl with trifluoropropyl groups. Final formulation of a potential wide temperature range hydraulic fluid is described.Presented as an American Society of Lubrication Engineers paper at the Lubrication Conference held in San Francisco, Calif., October 18–20, 1965.