A lubricating oil composition having a TBN in the range of 5 to 55 mg KOH/g and containing a major amount of a base oil of lubricating viscosity and a) 0.19 to 2.10 wt %, based on the total amount of the lubricating oil composition, of an overbased calcium carboxylate having a TBN of 100 mg KOH/g or more, wherein the wt % is expressed in terms of the calcium content; b) 0.002 to 0.06 wt %, based on the total amount of the lubricating oil composition, of a bis-succinimide compound, wherein the wt % is expressed in terms of the nitrogen content; and c) 0.007 to 0.15 wt %, based on the total amount of the lubricating oil composition, of a zinc dialkyldithiophosphate having a secondary alkyl group, wherein the wt % is expressed in terms of the phosphorus content.