| abstract |
A lubricating oil having an ashless nitrogenous TBN source together with ash containing detergent having a TBN in excess of 100, a source of magnesium, and metal dihydrocarbyl dithiophosphate with predominantly or exclusively secondary hydrocarbyl groups is described. It comprises a major amount of an oil of lubricating viscosity having a sulfated ash content between 0.35 and 2 mass percent and A) a nitrogenous TBN source selected from the group consisting of ashless nitrogen containing dispersants, ashless nitrogen containing dispersant viscosity modifiers, oil soluble aliphatic, oxyalkyl, or arylalkyl amines and mixtures thereof; B) a metal salt of an oil soluble acid having a TBN in excess of 100; C) at least 500 ppm (mass) magnesium; and D) at least one metal dihydrocarbyl dithiophosphate. The nitrogenous TBN source provides at least about 1.5 TBN to the finished lubricant. The metal salt of an oil soluble acid provides at least about 40 % of the total TBN of the composition. At least 50 mole percent of the hydrocarbyl groups on the dithiophosphate are secondary. Overbased magnesium solfonate may be used as the metal salt of an oil soluble sulfonic acid having a TBN in excess of 100 and the additive providing at least 500 ppm (mass) magnesium. The lubricant may be free of aromatic amines having at least two aromatic groups attached directly to the nitrogen. It may have at least 100 ppm (mass) boron and at least 1000 ppm (mass) phosphorus. The boron-to-nitrogen ratio is at least 0.1. |