Lubricant composition for diesel engines

This invention relates to lubricants suitable for use in diesel engines and to a method of controlling the viscosity of such lubricants in the presence of soot. This invention relates to a method of controlling the soot induced viscosity increase of a diesel engine lubricant composition comprising a base oil and a dispersant, by including in said lubricant composition an effective amount of an antioxidant, characterised in that the antioxidant comprises a dihydrocarbyldithiocarbamate of a metal selected from antimony, bismuth and mixtures thereof. The antioxidant may optionally contain at least one other compound selected from a phenolic and an aminic compound. The method of the present invention improves the performance retention of the dispersant additive, and thus inhibits the soot-induced viscosity increase of the lubricant.