Patent ID: 7253231

Claim:
A method of lubricating an internal combustion engine wherein said method comprises adding to a crankcase of said engine a lubricating oil composition comprising a major amount of an oil of lubricating viscosity and a minor amount of an additive reaction product prepared by a method comprising reacting an acylating agent with an olefin copolymer having a number average molecular weight greater than about 1,000 in the presence of a free radical initiator and said method being essentially free of hydrocarbon solvent in an extruder to provide a copolymer intermediate comprising an acylated olefin copolymer having a degree of grafting (DOG) of the acylating agent on the olefin copolymer of at least 0.5 wt. %, and wherein the copolymer intermediate is reduced in molecular weight; vacuum stripping unreacted components; pelletizing the copolymer intermediate to form a pelletized copolymer intermediate; dissolving the pelletized copolymer intermediate in a neutral oil to form a dissolved copolymer intermediate; and reacting the dissolved copolymer intermediate with an amine to provide a grafted olefin copolymer additive reaction product, wherein the lubricating oil composition achieves a weighted demerits-1P (WDP) value of less than 250, a top land carbon (TLC) value of less than 20, and a top groove carbon (TGC) value of less than 20, in the Caterpillar 1P Test Method.