Patent ID: 8642524

Claim:
A method for controlling soot-induced viscosity increase experienced in diesel engine lubricating oils during use in diesel engines while not adversely affecting the viscosity-modifying effect of polymeric viscosity improvers included in the lubricating oil, the method comprising: (a) employing as the diesel engine lubricating oil an oil formulation comprising a base oil blend consisting essentially of a Group I base stock, base oil or mixtures thereof and from about 20 to about 80 wt % of a GTL base stock or base oil; and (b) wherein said oil formulation includes about 15%, based on the total weight of the oil formulation of a polymeric viscosity-modifying additive comprising a copolymer of ethylene and propylene, which when used in said amount, provides the oil formulation with a % viscosity increase from soot of from about 24 to 73% and a thickening parameter in the range of about 1.57 to about 1.77.