Lubricating oil compositons

Abstract

Disclosed is a natural gas engine lubricating oil composition which comprises: (a) a major amount of an oil of lubricating viscosity having a kinematic, (b) greater than about 2 wt. % but less than about 4 wt. %, based on the total weight of the natural gas engine lubricating oil composition, of one or more phenolic antioxidants, (c) about 0.1 to about 1 wt. %, based on the total weight of the natural gas engine lubricating oil composition, of one or more aminic antioxidants, (d) one or more metal dithiophosphates, and (e) one or more alkali metal or alkali earth metal phenate detergents having a TBN of about 150 to about 250 on an oil free basis, wherein the one or more alkali metal or alkali earth metal phenate detergents provide at least about 0.10 wt. % of alkali metal or alkali earth metal to the natural gas engine lubricating oil composition.

What is claimed is: 
     
         1 . A natural gas engine lubricating oil composition comprising:
 (a) a major amount of an oil of lubricating viscosity,   (b) greater than about 2 wt. % but less than about 4 wt. %, based on the total weight of the natural gas engine lubricating oil composition, of one or more phenolic antioxidants,   (c) about 0.1 wt. % to about 1 wt. %, based on the total weight of the natural gas engine lubricating oil composition, of one or more aminic antioxidants,   (d) one or more metal dithiophosphates,   (e) one or more alkali metal or alkali earth metal phenate detergents having a total base number (TBN) of about 150 to about 250 on an oil free basis, wherein the one or more alkali metal or alkali earth metal phenate detergents provide at least about 0.10 wt. % of alkali metal or alkali earth metal to the natural gas engine lubricating oil composition,   
     
     
         2 . The natural gas engine lubricating oil composition of  claim 1 , having a TBN of about 5 to about 8 as determined by ASTM D 2896. 
     
     
         3 . The natural gas engine lubricating oil composition of  claim 1 , having a TBN of about 6 to about 7 as determined by ASTM D 2896. 
     
     
         4 . The natural gas engine lubricating oil composition of  claim 1 , having a sulfated ash content of about 0.65 to about 0.8 wt. % as determined by ASTM D 874. 
     
     
         5 . The natural gas engine lubricating oil composition of  claim 1 , wherein the major amount of the oil of lubricating viscosity is greater than 50 wt. %, based on the total weight of the lubricating oil composition. 
     
     
         6 . The natural gas engine lubricating oil composition of  claim 1 , wherein the one or more phenolic antioxidants are one or more sterically hindered phenolic antioxidants. 
     
     
         7 . The natural gas engine lubricating oil composition of  claim 1 , wherein the one or more aminic antioxidants are one or more diphenylamine antioxidants. 
     
     
         8 . The natural gas engine lubricating oil composition of  claim 1 , wherein the one or more metal dithiophosphates are one or more zinc dithiophosphates. 
     
     
         9 . The natural gas engine lubricating oil composition of  claim 1 , wherein the one or more metal dithiophosphates are one or more zinc dialkyl dithiophosphate compounds derived from a primary alcohol. 
     
     
         10 . The natural gas engine lubricating oil composition of  claim 1 , comprising about 0.01 wt. % to about 0.3 wt. % of phosphorus derived from the one or more metal dithiophosphates, based on the total weight of the lubricating oil composition. 
     
     
         11 . The natural gas engine lubricating oil composition of  claim 1 , wherein the one or more alkali metal or alkali earth metal phenate detergents provide at least about 0.12 wt. % of alkali metal or alkali earth metal to the natural gas engine lubricating oil composition. 
     
     
         12 . The natural gas engine lubricating oil composition of  claim 1 , wherein the one or more alkali metal or alkali earth metal phenate detergents are one or more calcium phenate detergents. 
     
     
         13 . The natural gas engine lubricating oil composition of  claim 1 , wherein the one or more alkali metal or alkali earth metal phenate detergents are one or more sulfurized calcium phenate detergents. 
     
     
         14 . The natural gas engine lubricating oil composition of  claim 1 , further comprising at least one additive selected from the group consisting of antioxidants, rust inhibitors, dehazing agents, metal detergents, demulsifying agents, metal deactivating agents, friction modifiers, pour point depressants, antifoaming agents, co-solvents, corrosion-inhibitors, ashless dispersants, multifunctional agents, dyes, extreme pressure agents and mixtures thereof. 
     
     
         15 . A method for preventing or inhibiting deposit formation in a natural gas engine containing one or more steel pistons comprising the step of operating the natural gas engine with a natural gas engine lubricating oil composition comprising:
 (a) a major amount of an oil of lubricating viscosity,   (b) greater than about 2 wt. % but less than about 4 wt. %, based on the total weight of the natural gas engine lubricating oil composition, of one or more phenolic antioxidants,   (c) about 0.1 wt. % to about 1 wt. %, based on the total weight of the natural gas engine lubricating oil composition, of one or more aminic antioxidants,   (d) one or more metal dithiophosphates, and   (e) one or more alkali metal or alkali earth metal phenate detergents having a total base number (TBN) of about 150 to about 250 on an oil free basis, wherein the one or more alkali metal or alkali earth metal phenate detergents provide at least about 0.10 wt. % of alkali metal or alkali earth metal to the natural gas engine lubricating oil composition.   
     
     
         16 . The method of  claim 15 , wherein the natural gas engine lubricating oil composition has a TBN of about 5 to about 8 and a sulfated ash content of about 0.65 to about 0.8 wt. % as determined by ASTM D 874. 
     
     
         17 . The method of  claim 15 , wherein the one or more phenolic antioxidants are one or more sterically hindered phenolic antioxidants, the one or more aminic antioxidants are one or more diphenylamine antioxidants, and the one or more metal dithiophosphates are one or more zinc dithiophosphates. 
     
     
         18 . The method of  claim 15 , wherein the natural gas engine lubricating oil composition comprises about 0.01 wt. % to about 0.3 wt. % of phosphorus derived from the one or more metal dithiophosphates, based on the total weight of the lubricating oil composition. 
     
     
         19 . The method of  claim 15 , wherein the one or more alkali metal or alkali earth metal phenate detergents are one or more sulfurized calcium phenate detergents. 
     
     
         20 . The method of  claim 15 , wherein the lubricating oil composition further comprises at least one additive selected from the group consisting of antioxidants, rust inhibitors, dehazing agents, demulsifying agents, metal deactivating agents, friction modifiers, pour point depressants, antifoaming agents, co-solvents, corrosion-inhibitors, ashless dispersants, multifunctional agents, dyes, extreme pressure agents and mixtures thereof. 
     
     
         21 . The method of  claim 15 , wherein the deposit formed in the natural gas engine is less than 12 mg.