Abstract: A lubricating oil composition for transmissions is provided which improves fuel saving properties and has excellent metal fatigue life and heat resistance. The composition contains 50 to 97 percent by mass of (A) a mineral base oil having a 100° C. kinematic viscosity of 1.5 mm2/s or higher and 3.5 mm2/s or lower, a pour point a ?25° C. or lower, a viscosity index of 105 or greater, a % CP of 85 or greater, a % CN of 2 or greater and 20 or less and a % CA of 3 or less; 3 to 10 percent by mass of (B) a monoester-based base oil having a 100° C. kinematic viscosity of 2 mm2/s or higher and 10 mm2/s or lower; and 150 to 400 ppm by mass as phosphorus of (C) a specific sulfur-containing phosphite ester. The composition has a 100° C. kinematic viscosity of 2.5 mm2/s or higher and 4.0 mm2/s or lower.

Abstract: This invention concerns a process for preparing a sulfurized olefin containing reduced amounts of thiones using a low molecular weight hydrocarbon to precipitate the thiones from the sulfurized olefin.