Lubricating oil composition for marine engines

Abstract

The lubricating compositions of the present invention are designed for use in a four stroke outboard marine engine and contain an oil of lubricating viscosity, an ashless dispersant, a metal detergent, a rust inhibitor system comprising a combination of certain rust inhibitors with an ethoxylated alkyl phenol, a relatively high amount of ZDDP, and an amount of a molybdenum compound sufficient to provide the composition with 15-1,000 ppm by mass of molybdenum. An amount of about 15 ppm to 1,000 ppm by mass of molybdenum from a molybdenum compound has been found to be effective as an antiwear agent in combination with the high levels of ZDDP.

What is claimed is:  
     
         1 . A lubricating oil composition suitable for use in a four stroke marine engine which comprises an oil of lubricating viscosity containing an admixture of 
 (a) 1-3.75 wt. % of an ashless dispersant;    (b) a metal detergent;    (c) an oil soluble molybdenum compound in an amount sufficient to provide 15-1,000 ppm molybdenum in the composition;    (d) a zinc dialkyl dithiophosphate in an amount sufficient to provide at least 1,200 ppm phosphorus in the composition;    (e) a rust inhibitor system comprising (i) as a first rust inhibitor, an ethoxylated C 4 -C 18  alkyl phenol having 2-10 moles of ethylene oxide per mole in combination with a second rust inhibitor selected from the group consisting of (ii) a glycerol ester of a C 8 -C 22  fatty acid, (iii) a half ester of a C 8 -C 22  alkyl or alkenyl succinic acid and a C 2 -C 4  alkylene glycol and (iv) a C 8 -C 22  alkyl or alkenyl succinic acid or anhydride; and    (f) optionally, a viscosity modifier, said composition having a NOACK volatility less than 15%.    
     
     
         2 . The composition of  claim 1  wherein the second rust inhibitor is the glycerol ester and the composition further comprises a third rust inhibitor selected from the group consisting of (i) a half ester of a C 8 -C 22  alkyl or alkenyl succinic acid and a C 2 -C 4  alkylene glycol and (ii) a C 8 -C 22  alkyl or alkenyl succinic acid or anhydride.  
     
     
         3 . The composition of  claim 1  wherein the glycerol ester is a mixture comprising about 55 wt. % glycerol monooleate, 40 wt. % glycerol dioleate and about 5 wt. % glycerol trioleate.  
     
     
         4 . The composition of  claim 1  wherein the ethoxylated alkyl phenol is the 4 mole ethoxylate of nonylphenol.  
     
     
         5 . The composition of  claim 1  wherein the half ester is propylene glycol dodecyl succinate.  
     
     
         6 . The composition of  claim 1  wherein the alkyl or alkenyl succinic acid or anhydride is dodecyl or isomerized octadecenyl succinic acid anhydride.  
     
     
         7 . The composition of  claim 1  wherein each rust inhibitor is present in a range of 0.05 to 1.5 wt. % of the composition.  
     
     
         8 . The composition of  claim 4  wherein the second rust inhibitor is dodecyl succinic acid, and each rust inhibitor is present in the range of 0.10 to 0.40 wt. %.  
     
     
         9 . The composition of  claim 1  wherein the metal detergent is a calcium sulfonate or a calcium phenate or mixtures thereof.  
     
     
         10 . The composition of  claim 1  wherein the dispersant is a polyisobutenyl succinimide wherein the polyisobutenyl has an Mn of 1600-2500.  
     
     
         11 . The composition of  claim 1  wherein the molybdenum compound is a molybdenum dithiocarbamate.  
     
     
         12 . The composition of  claim 1  wherein the molybdenum compound is a trinuclear compound of the formula Mo 3 S k L n Q z  wherein L represents oil soluble organo groups, n is 1-4, k is 4-7 and Q is a neutral electron donating compound and z is 0.5.  
     
     
         13 . The composition of  claim 1  wherein the zinc dialkyl dithiophosphate is present in an amount sufficient to provide up to 2,000 ppm P in the composition.  
     
     
         14 . The composition of  claim 13  wherein the zinc dialkyl dithiophosphate comprises secondary alkyl groups having 2 to 8 carbon atoms.  
     
     
         15 . The composition of  claim 1  wherein the viscosity modifier is shear stable and is present in an amount of 0.5 to 5.0 wt. %.  
     
     
         16 . The composition of  claim 1  further comprising one or more phosphorus-free antioxidants.  
     
     
         17 . The composition of  claim 1  further comprising an antifoam agent.  
     
     
         18 . The composition of  claim 1  further comprising a lube oil flow improver.  
     
     
         19 . A method of operating and lubricating a four cycle marine engine which comprises supplying to the engine the lubricating oil composition of claims  1 - 18 .