Lubricating oil composition for automatic transmission

Abstract

This invention provides a lubricating oil composition for automobile transmission that includes: as low-viscosity base oils: (i) between 45 and 95 mass % of a Fischer-Tropsch synthetic low-viscosity base oil with a 100° C. kinematic viscosity of between 1 mm/s and 2 mm/s, and between 0 and 25 mass % of other than a Fischer-Tropsch synthetic low-viscosity base oil with a 100° C. kinematic viscosity of between 1 mm/s and 2 mm/s, and (ii) between 0 and 35 mass % of a base oil wherein the 100° C. kinematic viscosity is greater that 2 mm/s and no greater than 5 mm/s; and (iii) between 5 and 55 mass % of an olefin polymer or copolymer, as a high-viscosity base oil, wherein the 100° C. kinematic viscosity is between 100 and 800 mm/s. A lubricating oil composition for an automatic transmission wherein the 100° C. kinematic viscosity of this composition is between 3.8 and 5.5 mm/s, the viscosity index is no less than 190, the flashpoint is no less than 140° C., and the reduction ratio of the 100° C. kinematic viscosity after shear stability testing, at 60° C. for 20 hours, is maintained at no greater than 3%.