Method of improving the acrylic rubber sealant compatibility in an internal combustion engine

Abstract

It has been discovered that a lubricating oil composition containing a certain combination of a nitrogen-containing dispersant and a metal-containing detergent of an alkali metal salt of alkylphenol derivative having a Mannich base structure, together with a phosphorus-containing organic compound, can be effectively employed in a method for improving the acrylic rubber sealant compatibility in an internal combustion engine, if the ratio of the nitrogen-containing dispersant and a metal-containing detergent of an alkali metal salt of alkylphenol derivative having a Mannich base structure is adjusted to a specific range, i.e., in the range of from 1:0.005 to 1:2 in terms of the nitrogen contents.

1 . A method of improving the acrylic rubber sealant compatibility in an internal combustion engine, said method comprising contacting the acrylic rubber sealant in the internal combustion engine and operating the internal combustion engine with a lubricating oil composition comprising: 
 a) a major amount of a base oil of lubricating viscosity,    b) a nitrogen-containing ashless dispersant in an amount of 0.01 to 0.3 wt. % in terms of the nitrogen content, based on the total amount of the lubricating oil composition,    c) a metal-containing detergent of an alkali metal or alkaline earth metal salt of alkylphenol derivative having a Mannich base structure in an amount of 0.001 to 0.04 wt. % in terms of the metal content, based on the total amount of the lubricating oil composition, and    d) a phosphorus-containing organic compound in an amount of 0.001 to 0.5 wt. % in terms of the phosphorus content, based on the total amount of the lubricating oil composition,    wherein the ratio of components bi) to c) is in the range of from 1:0.005 to 1:2 in terms of the nitrogen content.    
   
   
       2 . The method according to  claim 1 , wherein the nitrogen-containing ashless dispersant is an alkenyl- or alkyl-succinic imide or a derivative thereof.  
   
   
       3 . The method according to  claim 1 , wherein the metal-containing detergent of an alkali metal or alkaline earth metal salt of alkylphenol derivative having a Mannich base structure is represented by the following formula:  
     
       
         
         
             
             
         
       
     
     wherein R is an alkyl group having 8 to 30 carbon atoms, and n is 0 or a positive integer.  
   
   
       4 . The method according to  claim 1 , wherein the phosphorus-containing organic compound is selected from the group consisting of zinc dihydrocarbyldithiophosphates, zinc dihydrocarbylphosphates, phosphoric acid esters, phosphorous acid esters, and thiophosphoric acid esters.  
   
   
       5 . The method according to  claim 1 , wherein the amount of the nitrogen-containing ashless dispersant is in the range of 0.01 to, 0.1 wt. % in terms of the nitrogen content, based on the total amount of the lubricating oil composition.  
   
   
       6 . The method according to  claim 1 , wherein the amount of the metal-containing detergent of an alkali metal or alkaline earth metal salt of alkylphenol derivative having a Mannich base structure is in the range of 0.002 to 0.1 wt. % in terms of the nitrogen content, based on the total amount of the lubricating oil composition.  
   
   
       7 . The method according to  claim 1 , wherein the amount of the phosphorus-containing organic compound is in the range of 0.01 to 0.2 wt. % in terms of the phosphorus content, based on the total amount of the lubricating oil composition.  
   
   
       8 . The method according to  claim 1 , further comprising a metal-containing detergent selected from the group consisting of alkali metal or alkaline earth metal salicylates, carboxylates, phenates and sulfonates in an amount of 1.0 wt. % or less in terms of the metal content, based on the total amount of the lubricating oil composition.  
   
   
       9 . The method according to  claim 8 , wherein the amount of metal-containing detergent selected from the, group consisting of alkali metal or alkaline earth metal salicylates, carboxylates, phenates and sulfonates arid the amount of the metal-containing detergent of an alkali metal or alkaline earth metal salt of alkylphenol derivative having a Mannich base structure is in a ratio of 1:0.003 to 1:1 in terms of the metal content.  
   
   
       10 . The method according to  claim 1 , further comprising a molybdenum compound selected from the group consisting of an oxymolybdenum complex prepared by the reaction between an acidic molybdenum compound and a basic nitrogen compound, sulfurized oxymolybdenum dithiocarbamate, and sulfurized oxymolybdenum dithiophosphate, in amount of 0.25 wt. % or less in terms of the molybdenum content, based on the total amount of the lubricating oil composition.  
   
   
       11 . The method according to  claim 1 , further comprising an alkali metal borate in an amount of 2 wt. % or less, based on the total amount of the lubricating oil composition.  
   
   
       12 . The method according to  claim 1 , further comprising an oxidation inhibitor selected from the group consisting of hindered phenol compounds and diarylamine compounds in an amount of 5 wt. % or less, based on the total amount of the lubricating oil composition.  
   
   
       13 . The method according to  claim 1 , wherein the base oil contains 10 wt. % or more of a mineral oil showing the following characteristics: 
 17 wt. % or less evaporation loss according to ASTM D-5800    90 wt. % or more saturated content,    10 wt. % or less, aromatic component,    0.01 wt. % or less, sulfur content, and    120 or more viscosity index.    
   
   
       14 . The method according to  claim 1  wherein the lubricating oil composition is a SAE viscosity grade selected from the group 1:5 consisting of 0W20, 0W30, 5W20, 5W30 and 10W30.  
   
   
       15 . The method according to  claim 14 , wherein the lubricating oil composition is a SAE viscosity grade selected from the group consisting of 10W30.