Patent ID: 7309681

Claim:
A method for the lubrication of a natural gas-fired engine comprising lubricating the engine with an ashless lubricating oil comprising: (i) a major amount of a lubricating oil base stock having a viscosity suitable for a natural gas-fired engine in the range of about 5 to about 16 cSt at 100° C., (ii) an effective amount of an ashless antioxidant additive combination comprising both a phenolic antioxidant and an alkylthiocarbamoyl compound in the mass ratio in the range of about 5:1 to 1:5; and (iii) an effective amount of an ashless phosphorous antiwear additive, wherein the oxidation resistance, nitration resistance and resistance to viscosity increase are all improved as compared to lubricating the engine with a lubricating oil composition which does not contain all three additives.