The present invention is directed to a method for controlling soot induced viscosity increase in diesel engines, by using as the diesel engine lubricant an oil formulation comprising a base oil containing about 10 to 80 wt % GTL base stock and/or base oil and/or hydrodewaxed or hydroisomerized/catalytic (or solvent) dewaxed base stock and/or base oil in combination with 20 to 90 wt % conventional Group I petroleum derived base oil, said base oil being further combined with a polymeric viscosity modifier, and to the lubricating oil which effects such control over soot induced viscosity increase.