A low viscosity lubricating oil composition having a CCS viscosity less than 3500 mPa.s at −25° C. and having no more than 0.16 mass % of phosphorus which comprises a dispersant, and a detergent of calcium or magnesium or both; and optionally a zinc dihydrocarbyldithiophosphate, a viscosity modifier, a pour point depressant and an antioxidant. The oil satisfies the Cummins M11 cross-head wear engine test specification in a low phosphorus and low viscosity formulation.