Lubricating oil compositions

Abstract

A heavy duty diesel engine lubricating oil composition comprising, or made by admixing: (A) a major amount of an oil of lubricating viscosity comprising at least 35 mass % of a Group III basestock, based on the mass of the oil of lubricating viscosity, that contains at most 0.03 mass % of sulfur, based on the mass of the basestock, and that has a viscosity index of 120 or greater and has greater than or equal to 90 mass % saturates, based on the mass of said basestock; and (B) a minor amount of an additive composition comprising: (i) a detergent composition; and (ii) one or more other additives; wherein the oil composition has a cold cranking simulated viscosity, measured according to ASTM D2602, of less than 7000 mPa.s at −25° C. and a sulfated ash, measured according to ASTM D874, of less than 1.35 mass %, based on the mass of the oil composition. The oil compositions provide improved piston cleanliness of a heavy duty diesel engine.

1 . A heavy duty diesel engine lubricating oil composition comprising, or made by admixing: 
 (A) a major amount of an oil of lubricating viscosity comprising at least 35 mass % of a Group III basestock, based on the mass of the oil of lubricating viscosity, that contains at most 0.03 mass % of sulfur, based on the mass of said basestock, and that has a viscosity index of 120 or greater and has greater than or equal to 90 mass % saturates, based on the mass of said basestock; and    (B) a minor amount of an additive composition comprising: 
 (i) a detergent composition; and  
 (ii) one or more other additives;  
 wherein the oil composition has a cold cranking simulated viscosity, measured according to ASTM D2602, of less than 7000 mPa.s at −25° C. and a sulfated ash content, measured according to ASTM D874, of less than 1.35 mass %, based on the mass of the oil composition.  
   
     
     
         2 . The oil composition according to  claim 1  wherein the oil of lubricating viscosity consists essentially of a Group III basestock and one or more of a Group IV basestock and a Group V basestock in the form of an ester.  
     
     
         3 . The oil composition according to  claim 1  wherein the detergent composition comprises a magnesium detergent additive and/or a calcium detergent additive.  
     
     
         4 . The oil composition according to  claim 3  further comprising a zinc dihydrocarbyl dithiophosphate additive.  
     
     
         5 . A method of lubricating a heavy duty diesel engine, which engine has a total displacement of at least 6.5 litres and a displacement per cylinder of at least 1.0 litre per cylinder, which method comprises supplying to the engine a lubricating oil composition as defined in  claim 1 .  
     
     
         6 . A combination of a heavy duty diesel engine, which engine has a total displacement of at least 6.5 litres and a displacement per cylinder of at least 1.0 litre per cylinder and a lubricating oil composition as defined in  claim 1 .  
     
     
         7 . A method of improving the piston cleanliness of an engine, which method comprises lubricating the engine with a lubricating oil composition as defined in  claim 1 .  
     
     
         8 . A heavy duty diesel engine lubricating oil composition giving at least 25 piston cleanliness merit points and not greater than 4% boost pressure loss in the OM441LA engine test, according to the CEC-L-52-T-97 procedure, which oil composition comprises, or is made by admixing: 
 (A) a major amount of an oil of lubricating viscosity; and    (B) a minor amount of an additive composition comprising: 
 (i) a detergent composition; and  
 (ii) one or more other additives;  
 wherein the oil composition has a cold cranking simulated viscosity, measured according to ASTM D2602, of less than 7000 mPa.s at −25° C. and a sulfated ash content, measured according to ASTM D874, of less than 1.35 mass %, based on the mass of the oil composition.