Hydrocarbon/silicon oil lubricating compositions for low temperature use

A lubricating oil composition comprising a homogeneous mixture of from 1% to 50% by weight of (A) poly(dimethylsiloxane) having the general formula:

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• when R is a methyl group in essentially all cases and n has a value such that the average viscosity of the poly(dimethylsiloxane) at 100.degree. F is between 10,000 cs and 1,000,000 cs, and the remainder of said mixture consisting of (B) hydrocarbon oil having a viscosity of less than 40,000 cs at -65.degree. F, and a flashpoint higher than 175.degree. F, and said hydrocarbon oil being at least one selected from the group consisting of (a) alkenes, (b) isoparaffins, and (c) naphthenics having a single ring which has multiple alkyl substituents;
• in the case of (a) and (b), the longest carbon chain, and in the case of (c) any alkyl substituent in which the longest carbon chain exceeds five carbon atoms, has multiple substituent alkyl branches, and its methyl branched homolog has a solubility parameter of less than 7.84 and said substituent alkyl branches of four or more carbon atoms are themselves branched, and where at least 50% of said substituent alkyl branches are bonded to carbons of the longest carbon chain which are immediately adjacent, or separated by only one carbon atom.