Abstract: Soot induced kinematic viscosity increase of lubricating oil compositions for diesel engines, particularly heavy duty diesel engines, equipped with EGR systems, particularly EGR systems operating in a condensing mode, can be ameliorated by addition of a phenylenediamine compound.

Abstract: A method of improving the seal compatibility and/or copper corrosion performance of lubricating oil compositions for the lubrication of the crankcases of an internal combustion engine, which method includes the step of adding to the lubricating oil compositions a minor amount of a non-hydrogenated (unsaturated) olefin polymer. Also described are lubricating oil compositions for engines and transmissions, which compositions contain sulphur and/or a salicylate soap and a minor amount of a non-hydrogenated (unsaturated) polymer, which compositions are compatible with nitrile rubber engine and transmission seals and copper-containing engine and transmission components.

Abstract: Linked aromatic compounds found to act as potent soot dispersants in lubricating oil compositions; lubricating oil compositions containing such soot dispersants and precursor compounds from which the soot dispersants are derived.