Aminic antioxidants to minimize turbo sludge

1. A method for lubricating a spark ignited, turbo-charged, sump-lubricated internal combustion engine with a lubricant, wherein the lubricant encounters a temperature within the turbocharger of at least 300° C., wherein said lubricant is contaminated with liquid fuel and wherein the lubricant is subject to deterioration as revealed by the formation of granular sediment, said method comprising providing said engine with a lubricant which contains an amount of an aminic antioxidant effective to reduce the formation of said granular sediment, said amount being at least about 0.5 percent by weight of the lubricant, and wherein the lubricant contains less than about 2 percent by weight of a hindered phenolic antioxidant; wherein the engine is fueled with a gasoline which comprises greater than about 5 percent by weight of aromatic materials having one or more hydrocarbyl substituents totaling 3 or more carbon atoms.

2. The method of claim 1 wherein said liquid fuel comprises greater than about 5 percent by weight content of cyclic materials boiling above about 150° C.

3. The method of claim 1 wherein said liquid fuel has a sulfur content of less than or equal to about 50 parts per million by weight.

4. The method of claim 1 wherein the amount of aminic antioxidant is at least about 1 percent by weight of the lubricant.

5. The method of claim 1 wherein the amount of phenolic antioxidant in the lubricant is less than about 0.5 percent by weight of the lubricant.

6. The method of claim 1 wherein the amount of aminic antioxidant in the lubricant is greater than the amount of the hindered phenolic antioxidant.

7. The method of claim 1 wherein the lubricant comprises at most about 60 percent by weight of an API Group I oil.

8. The method of claim 1 wherein the lubricant further comprises a rust inhibitor or an oil-soluble alkali metal salt.