Detergent systems for oxidation resistance in lubricants

A method of maintaining a stable viscosity in a lubricating composition upon oxidization, the method comprising:

• performing an oxidization test pursuant to GFC Lu-43-A-11 on a lubricating composition;
• the lubricating composition including one or more base oils of lubricating viscosity, sulfurized additives providing at least about 1,500 ppm sulfur, one or more boronated dispersants providing about 40 ppm to about 500 ppm of boron, and a detergent system providing about 0.2 to about 1.0 weight percent soap to the lubricating composition and providing magnesium, sodium, and calcium, wherein the detergent system provides greater than about 90 ppm of sodium and no more than about 1,000 ppm of magnesium to the lubricating composition, and wherein the detergent system has a weight ratio of sodium-to-magnesium of about 0.4 to 2.0, and a weight ratio of sulfur-to-sodium of about 12 or less;
• wherein the lubricating composition exhibits a viscosity increase upon oxidization after 144 hours of no greater than about 150 percent when tested pursuant to GFC Lu-43-A-11;
• and
• wherein the lubricating composition includes about 90 ppm to about 1,000 ppm of sodium, about 500 ppm to about 2,000 ppm of calcium, about 100 to about 1,000 ppm of magnesium, about 1,500 to about 4,000 ppm of sulfur, and a weight ratio of calcium-to-magnesium of about 0.5 to about 2.5.