Marine engine lubrication

Abstract

Two-stroke cross-head marine compression-ignited engine system lubrication is effected by a composition comprising a major amount of an oil of lubricating viscosity containing at least 50 mass % of a basestock containing greater than or equal to 90% saturates and less than or equal to 0.03% sulphur or a mixture thereof, and respective minor amounts of an oil-soluble overbased metal alkyl salicylate detergent and an oil-soluble polyalkenyl-substituted carboxylic acid anhydride or an oil-soluble alkylated phenol. The presence of the anhydride or the phenol improves asphaltene dispersency in the lubricant.

What is claimed is: 
     
         1 . A system lubricating oil composition for a two-stroke cross-head marine compression-ignited engine, the composition having a TBN of less than 18 and comprising, or being made by admixing:
 (A) an oil of lubricating viscosity, in a major amount, 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;   (B) an oil-soluble overbased metal alkyl salicylate detergent, in a minor amount; and   (C) in a minor amount, an oil-soluble polyalkenyl-substituted carboxylic acid anhydride, the, or at least one, polyalkenyl group being derived from a polyalkene having a number average molecular weight of from 200 to 3,000, or an oil-soluble alkylated phenol.   
     
     
         2 . The system lubricating oil composition of  claim 1  where the oil of lubricating viscosity contains more than 60 mass % of a basestock containing greater than or equal to 90% saturates and less than or equal to 0.03% sulphur or a mixture thereof. 
     
     
         3 . The system lubricating oil composition of  claim 1  where the basestock is a Group II, Group III or Group IV basestock. 
     
     
         4 . The system lubricating oil composition of  claim 1  where (B) is C 9  to C 30  alkyl-substituted. 
     
     
         5 . The system lubricating oil composition of  claim 1  where the polyalkenyl substituent in (C) has from 8 to 400 carbon atoms. 
     
     
         6 . The system lubricating oil composition of  claim 5  where the polyalkenyl substituent in (C) has from 12 to 100 carbon atoms. 
     
     
         7 . The system lubricating oil composition of  claim 6  where the polyalkenyl substituent in (C) has from 16 to 64 carbon atoms. 
     
     
         8 . The system lubricating oil composition of  claims 1  where the polyalkenyl substituent in (C) has a number average molecular weight of from 350 to 1000, 
     
     
         9 . The system lubricating oil composition of  claims 1  where the polyalkenyl substituent in (C) has a number average molecular weight of from 500 to 1000, 
     
     
         10 . The system lubricating oil compositions of  claim 1  where the polyalkenyl-substituted carboxylic acid anhydride in (C) is a succinic anhydride. 
     
     
         11 . The system lubricating oil composition of  claim 10  where (C) is a polybutene succinic anhydride. 
     
     
         12 . The system lubricating oil composition of  claim 1  where (C) is an oil-soluble alkylated phenol derived from cashew nut shell liquid (CNSL) 
     
     
         13 . The system lubricating oil composition of  claim 12  where (C) is a hydrogenated cardenol. 
     
     
         14 . The system lubricating oil composition of  claim 1  where (C) is a predominantly C 2  Friedel-Crafts alkylated phenol. 
     
     
         15 . The system lubricating oil composition of  claim 1 , wherein the TBN is more than 1. 
     
     
         16 . The system lubricating oil composition of  claim 15 , wherein the TBN is more than 3. 
     
     
         17 . The system lubricating oil composition of  claim 1 , wherein the TBN is more than 5. 
     
     
         18 . The system lubricating oil composition of  claim 1 , wherein the TBN is less than 10. 
     
     
         19 . A method of providing system lubrication to a two-stroke cross-head marine compression-ignited engine, which comprises lubricating the crankcase of the engine with a system lubricating oil composition of  claim 1 . 
     
     
         20 . A combination of the crankcase of a two-stroke cross-head marine compression-ignited engine and a system lubricating oil composition of  claim 1 .