Marine engine lubrication

Abstract

Lubricant additives comprising as overbased metal hydrocarbyl-substituted hydroxybenzoate detergent dispersed in diluent and a polyalkenyl-substituted carboxlic acid anhydride dispersed in a diluent oil containing 50 mass % or more of a basestock containing greater than or equal to 90% saturates and less than or equal to 0.03% sulphur or a mixture thereof are blended, in minor amounts, with a high saturates content oil of lubricating viscosity, in a major amount, to give trunk piston marine engine lubricating oil composition for a medium-speed four-stroke compression-ignited marine engine.

What is claimed is: 
     
         1 . A method of preparing a trunk piston marine engine lubricating oil composition for a medium-speed four-stroke compression-ignited marine engine comprising blending (A) a lubricant additive, in a minor amount, comprising an overbased metal hydrocarbyl-substituted hydroxybenzoate detergent dispersed in diluent and (B) an additive comprising a polyalkenyl-substituted carboxylic acid anhydride as active ingredient dispersed in a diluent oil containing 50 mass % or more of a basestock containing greater than or equal to 90% saturates and less than or equal to 0.03% sulphur or a mixture thereof with (C) an oil of lubricating viscosity in a major amount that comprises 50 mass % or more of a basestock containing greater than or equal to 90% saturates and less than or equal to 0.03% sulphur. 
     
     
         2 . The method of  claim 1  wherein the metal is calcium. 
     
     
         3 . The method of  claim 1 , wherein the hydrocarbyl-substituted hydroxybenzoate is a salicylate. 
     
     
         4 . The method of  claim 1 , wherein the hydrocarbyl group has from 8 to 400 carbon atoms. 
     
     
         5 . The method of  claim 1 , wherein the diluent oil in which (B) is dispersed comprises 60 mass % or more of the basestock containing greater than or equal to 90% saturates and less than or equal to 0.03% sulphur, or a mixture thereof. 
     
     
         6 . The method of  claim 5  wherein the diluent oil in which (B) is dispersed consists of or consists essentially of the basestock containing greater than or equal to 90% saturates and less than or equal to 0.03% sulphur or a mixture thereof. 
     
     
         7 . The method of  claim 1 , wherein the basestock is a Group II, III, IV or V basestock. 
     
     
         8 . The method of  claim 1 , wherein the polyalkenyl substituent in (B) has from 8 to 400 carbon atoms. 
     
     
         9 . The method of  claim 1 , wherein the polyalkenyl substituent in (B) has a number average molecular weight of from 350 to 1000. 
     
     
         10 . The method of  claim 1 , wherein the polyalkenyl-substituted carboxylic acid anhydride derivative, (B), is a succinic anhydride. 
     
     
         11 . The method of  claim 10 , wherein (B) is a polyisobutene succinic acid or anhydride. 
     
     
         12 . The method of  claim 1  wherein the diluent in (A) comprises 50 mass % or more of a basestock containing greater than or equal to 90% saturates and less than or equal to 0.03% sulphur. 
     
     
         13 . The method of  claim 1 , wherein the composition has a TBN of 20 to 60. 
     
     
         14 . The method of  claim 1 , wherein the basestock in the oil of lubricating viscosity (C) is a Group II, III, IV or V basestock. 
     
     
         15 . A trunk piston marine engine lubricating oil composition for a medium-speed four-stroke compression-ignited marine engine obtainable by the method of  claim 1 . 
     
     
         16 . A method of operating a trunk piston medium-speed compression-ignited marine engine comprising
 (i) making a lubricating oil composition by the method of  claim 1 ;   (ii) fuelling the engine with a heavy fuel oil; and   (iii) lubricating the crankcase of the engine with said lubricating oil composition.   
     
     
         17 . A lubricant additive (B) as defined in  claim 1 . 
     
     
         18 . A combination or admixture of a lubricant additive (B) and a lubricant additive (A), wherein lubricant additive (B) and lubricant additive (A) are as defined in  claim 1 .