The present invention provides a lubricating oil composition comprising: (a) a major amount of a lubricating oil, (a) a diarylamine antioxidant, and (b) an amidine compound of Formula (I), wherein R1 is hydrogen, an alkyl or an aromatic group containing 1-30 carbon atoms; x is from 1 to 5; Y is an optional linking alkyl group; Z is carbon or nitrogen; and R2 is hydrogen or alkyl groups containing 1-30 carbon atoms. Also provided is a method for lubricating an engine comprising lubricating the engine with said lubricating oil composition.