Lubricating oil compositions comprising a biodiesel fuel and a Mannich condensation product

A lubricating oil composition contaminated with at least about 0.3 wt % of a biodiesel fuel or a decomposition product thereof, based on the total weight of the lubricating oil composition, wherein the lubricating oil composition comprises:

• a. a major amount of base oil of lubricating viscosity;
• and
• b. from 0.55 to 4.95 wt. % on an actives basis of a Mannich condensation product, wherein the Mannich condensation product is of the formula 7
• wherein each R is independently —CHR′—, wherein R′ is branched or linear alkyl having one to about 10 carbon atoms, cycloalkyl having from about 3 carbon atoms to about 10 carbon atoms, aryl having from about 6 carbon atoms to about 10 carbon atoms, alkaryl having from about 7 carbon atoms to about 20 carbon atoms, or aralkyl having from about 7 carbon atoms to about 20 carbon atoms, R1 is a polyisobutyl group derived from polyisobutene containing at least about 70 wt. % methylvinylidene isomer and having a number average molecular weight in the range of about 400 to about 2,500;
• X is hydrogen, an alkali metal ion, or alkyl having one carbon atom to about 6 carbon atoms;
• W is [CHR″]—m, wherein each R″ is independently H, alkyl having one carbon atom to about 15 carbon atoms, or a substituted-alkyl having one carbon atom to about 10 carbon atoms and one or more substituents selected from the group consisting of amino, amido, benzyl, carboxyl, hydroxyl, hydroxyphenyl, imidazolyl, imino, phenyl, sulfide, or thiol;
• and m is an integer from one to 4;
• Y is hydrogen, alkyl having one carbon atom to about 10 carbon atoms, —CHR′OH, wherein R′ is as defined above,
• or of formula 8:
• wherein Y′ is —CHR′OH, wherein R′ is as defined above;
• and R, X, and W are as defined above;
• Z is hydroxyl, a hydroxyphenyl group of the formula 9:
• or of formula 10:
• wherein R, R1, Y′, X, and W are as defined above,
• and n is an integer from 0 to 20, with the proviso that when n=0, Z must be of formula 10 as defined above, and
• c. optionally at least one dispersant present at from 0.85 to 5.13 wt. % on an actives basis.