Abstract: A method of reducing deposits in an internal combustion engine, comprising lubricating the internal combustion engine with a lubricating oil composition comprising lubricating oil base oil, one or more anti-wear additives and one or more poly(hydroxycarboxylic acid) amide salt derivatives preparable by reaction of an amine and a poly(hydroxycarboxylic acid) of formula (I) Y—CO[O-A-CO]n—OH ??(I) where Y is hydrogen or optionally substituted hydrocarbyl group, A is a divalent optionally substituted hydrocarbyl group and n is from 1 to 100, with an acid or a quaternizing agent.

Abstract: Oil composition is provided containing a major amount of a natural and/or synthetic base oil and, as a marking substance, a detectable level of one or more compounds of formula IV compound supported thereon, such that the marking substance gives a colour reaction A method for detecting the presence of a marking substance in an oil composition is provided, wherein the oil composition is contacted with a test strip having an acidic upon contact with the test strip.