Patent ID: 8754017

Claim:
A method for lubricating an engine fueled by natural gas, comprising adding thereto a lubricant composition comprising: (a) an oil of lubricating viscosity, (b) an overbased sodium sulfonate detergent in an amount to provide 0.015 to 0.1 weight percent sodium to the lubricant composition, wherein the sodium comprises about 10 to 27 percent by weight of the total metal content of the lubricant composition, (c) an overbased calcium detergent, in an amount to provide 0.05 to 0.3 percent by weight of calcium to the lubricant composition, (d) a succinimide dispersant, and (e) a zinc salt of a phosphorus acid; wherein the lubricant composition has a sulfated ash of 0.3 to less than about 0.8 percent and wherein the overbased sodium sulfonate detergent contributes about 15 to about 30 percent of the total sulfated ash of the composition.