A method for preventing or reducing engine knock or pre-ignition in a high compression spark ignition engine lubricated with a lubricating oil by introducing to a combustion chamber of the engine from 0.1 to 5% by volume of the gasoline used a lubricating oil as a formulated oil, said formulated oil having a composition comprising (i) a major amount of a lubricating oil base stock comprising at least 80% by weight of one branched ester having at least 15% of the total carbons in the form of methyl groups, and (ii) a minor amount of at least one ashless amine phosphate antiwear additive. Also provided is a lubricating engine oil for high compression spark ignition engines including (i) a major amount of a lubricating oil base stock comprising at least 80% by weight formula I below: ##STR00001##
esterified (per OH basis) with 25 to 100% isobutyric acid and 0 to 75% 3,5,5-trimethylhexanoic acid, wherein R is a H, methyl, ethyl, isopropyl, or isobutyl, and (ii) a minor amount of at least one amine phosphate ashless antiwear additive.

A method for preventing or reducing engine knock or pre-ignition in a high compression spark ignition engine lubricated with a lubricating oil by introducing to a combustion chamber of the engine from 0.1 to 5% by volume of the gasoline used a lubricating oil as a formulated oil, said formulated oil having a composition comprising (i) a major amount of a lubricating oil base stock comprising at least 80% by weight of one branched ester having at least 15% of the total carbons in the form of methyl groups, and (ii) a minor amount of at least one ashless amine phosphate antiwear additive. Also provided is a lubricating engine oil for high compression spark ignition engines including (i) a major amount of a lubricating oil base stock comprising at least 80% by weight formula I below:

##STR00001##

esterified (per OH basis) with 25 to 100% isobutyric acid and 0 to 75% 3,5,5-trimethylhexanoic acid, wherein R is a H, methyl, ethyl, isopropyl, or isobutyl, and (ii) a minor amount of at least one amine phosphate ashless antiwear additive.

The present invention relates to functional fluid compositions containing antioxidants, and specifically stable compositions containing antioxidants with limited solubility in and/or limited compatibility with the functional fluids with which they are used. In particular the present invention deals with functional fluids used in internal combustion engines, such as engine oils, and antioxidants containing a phenolic or benzoic group, where the antioxidant is present in the functional fluid composition at levels that would otherwise cause the composition to be unstable and/or hazy.