Lubricating oil composition for internal combustion engine

Abstract

A lubricating oil composition is provided as an engine oil for an internal combustion engine employing heat management. The composition includes (A) a base oil having 100° C. kinematic viscosity of 3.0 to 5.0 mm 2 /s, (B) a boronated succinimide in an amount of 0.007 mass percent or more as boron and in an amount of 5 mass percent or less as the succinimide ashless dispersant, based on total mass of the composition, (C) a phenol-based antioxidant in an amount of 0.5 mass percent or more, and (D) a viscosity index improver having a ratio of weight average molecular weight and PSSI of 1.2×104 or greater in an amount of 0.1 to 5 percent by mass. The composition has a 150° C. HTHS viscosity of 2.0 to 2.8 mPa·s, a 100° C. HTHS viscosity of 4.8 mPa·s or lower and a viscosity index of 180 or greater.

1 . A lubricating oil composition for an internal combustion engine, the composition comprising (A) a base oil having 100° C. kinematic viscosity of 3.0 to 5.0 mm 2 /s, (B) a boronated succinimide in an amount of 0.007 percent by mass or more as boron and in an amount of 5 percent by mass or less as the succinimide ashless dispersant, on the basis of the total mass of the composition, (C) a phenol-based antioxidant in an amount of 0.5 percent by mass or more, and (D) a viscosity index improver having a ratio of weight average molecular weight and PSSI of 1.2×104 or greater in an amount of 0.1 to 5 percent by mass, the composition having a 150° C. HTHS viscosity of 2.0 to 2.8 mPa·s, a 100° C. HTHS viscosity of 4.8 mPa·s or lower and a viscosity index of 180 or greater. 
     
     
         2 . The lubricating oil composition for an internal combustion engine according to  claim 1 , wherein a ratio of the boronated succinimide to a non-boronated succinimide is from 1.0 to 3.0 by weight. 
     
     
         3 . The lubricating oil composition for an internal combustion engine according to  claim 1 , wherein a ratio of a total content of the boronated succinimide and the non-boronated succinimide to a content of the viscosity index improver is 6 or less. 
     
     
         4 . The lubricating oil composition for an internal combustion engine according to  claim 2 , wherein a ratio of a total content of the boronated succinimide and the non-boronated succinimide to a content of the viscosity index improver is 6 or less.