Lubricating oils having overbased calcium and overbased magnesium detergents, and methods for improving low speed preignition

摘要

A lubricating oil composition and a method of operating a boosted internal combustion engine. The lubricating oil comprises more than 50% by weight of a base oil, one or more overbased calcium-containing detergents, one or more overbased magnesium-containing detergents, and one or more molybdenum compounds. Provides a reduction in LSPI of more than 60% compared to the LSPI of the reference oil and passes the ball rust test. The ratio of the weight percent calcium from the overbased detergent to the weight percent magnesium from the overbased detergent is less than 11.9. The ratio of total ppm of magnesium to total TBN of the lubricating oil in mg KOH / g is greater than 19. The ratio of total ppm of calcium to total TBN of the lubricating oil is less than 222. The oils and methods can reduce low speed preignition events in boosted internal combustion as compared to commercially available lubricating oils.