Patent ID: 8138133

Claim:
A gear oil composition exhibiting improved fuel-savings effect and bearing fatigue life characteristics comprising: a first base oil comprising a mineral-based oil or a hydrocarbon-based synthetic oil selected from a poly-α-olefin, wherein said mineral-based oil and said hydrocarbon-based synthetic oil have a kinematic viscosity of 3.5 to 7 mm 2 /s at 100° C., a second base oil comprising a hydrocarbon-based synthetic oil having a kinematic viscosity of 20 to 52 mm 2 /s at 100° C., wherein the difference in the viscosity of the first base oil and the second base oil is at least 13 mm 2 /s and no more than 48.5 mm 2 /s, wherein the second base oil is a poly-α-olefin or an ethylene-α-olefin copolymer, and a sulfur-based additive incorporated at 1 to 5% by mass as elementary sulfur on the whole gear oil composition, wherein the gear oil composition has a kinematic viscosity of 70 to 80 mm 2 /s at 40° C., and is essentially free of viscosity index modifying additives, wherein the first base oil is present in the amount of 11 to 39% by mass and the second base oil is present in the amount of 33 to 61% by mass with the total of the first base oil and the second base oil being about 72% by mass of the gear oil composition, wherein the sulfur-based additive is a sulfided olefin, and wherein the kinematic viscosity at 40 deg. C. for measuring fuel-saving effect is less than or equal to 73.4 mm 2 /s and the oil film thickness for measuring bearing fatigue life is greater than or equal to 133 mm for the gear oil composition.