Low viscosity engine oil with superior engine wear protection

Abstract

An engine oil lubricant composition comprising a major amount of base oil and an effective amount of a zinc dialkyl dithio phosphate, a polymeric viscosity index improver and a mixture of alkaline earth metal detergents provides improved fuel efficiency while providing excellent wear in an engine.

What is claimed is: 
     
         1 . An engine oil lubricant composition comprising a major amount of base oil and a zinc dialkyl dithio phosphate at from 0.6 to 0.91 wt. %, a polymeric viscosity index improver at from 0.01 to 0.57 wt. % and a mixture of alkaline earth metal detergents at from 0.1 to 2.2 wt. %, wherein said engine oil lubricant composition has having a sulfated ash content of less than or equal to about 0.6 wt % and an HTHS of less than or equal to 2.8 cP at 150° C. 
     
     
         2 . The lubricant composition of  claim 1 , wherein the alkaline earth metal detergents are selected from metallic salicylates and sulfonates. 
     
     
         3 . The lubricant composition of  claim 2 , wherein the metallic salicylates and sulfonates are selected from calcium and magnesium. 
     
     
         4 . The lubricant composition of  claim 1 , wherein the polymeric viscosity index improver has a weight average molecular weight greater than about 500,000. 
     
     
         5 . The lubricant composition of  claim 4 , wherein the polymeric viscosity index improver has a number average molecular weight greater than about 300,000. 
     
     
         6 . The lubricant composition of  claim 1 , wherein the polymeric viscosity index improver is selected from a hydrogenated star polyisoprene, styrene-isoprene block co-polymer and ethylene-propylene copolymer. 
     
     
         7 . The lubricant composition of  claim 1 , wherein the ZDDP is a secondary dialkyl dithiophosphate. 
     
     
         8 . The lubricant composition of  claim 1 , further comprising a mixture of at least two dispersants wherein at least one dispersant is a borated succinimide. 
     
     
         9 . A engine oil lubricant composition comprising a major amount of base oil and an effective amount of a zinc dialkyl dithio phosphate, a polymeric viscosity modifier present in an amount of less than about 1.0 wt % solid polymer content and a mixture of detergents selected from salicylates and sulfonates, wherein said engine oil lubricant composition has having a sulfated ash content of less than about 0.8 wt %. 
     
     
         10 . A method for improving fuel efficiency and wear in an engine, said method comprising
 i) adding to said engine an engine oil lubricant composition having a sulfated ash content of less than or equal to about 0.6 wt % and an HTHS of less than or equal to 2.8 cP at 150° C., said lubricant composition comprising a zinc dialkyl dithio phosphate at from 0.6 to 0.91 wt. %, a polymeric viscosity modifier at from 0.01 to 0.57 wt. % and a mixture of alkaline earth metal detergents at from 0.1 to 2.2 wt. %.   
     
     
         11 . The method of  claim 10 , wherein the alkaline earth metal detergents are selected from metallic salicylates and sulfonates. 
     
     
         12 . The method of  claim 11 , wherein the metallic salicylates and sulfonates are selected from calcium and magnesium. 
     
     
         13 . The method of  claim 10 , wherein the polymeric viscosity index improver has a weight average molecular weight greater than about 500,000. 
     
     
         14 . The method of  claim 13 , wherein the polymeric viscosity index improver has a number average molecular weight greater than about 300,000. 
     
     
         15 . The method of  claim 10 , wherein the polymeric viscosity index improver is selected from a hydrogenated star polyisoprene, styrene-isoprene block co-polymer and ethylene-propylene copolymer. 
     
     
         16 . The method of  claim 1 , wherein the ZDDP is a secondary dialkyl dithiophosphate. 
     
     
         17 . The method of  claim 1 , further comprising a mixture of at least two dispersants wherein at least one dispersant is a borated succinimide.