Magnesium sulfonate detergent having improved compatibility with friction modifiers

A method of improving the storage stability of an overbased magnesium sulfonate detergent, the method comprising

• (a) preparing a mixture of a linear C14 to C24 alkyl benzene sulfonic acid or salt thereof, a molar excess of magnesium oxide or magnesium hydroxide, a C1 to C13 alcohol, and one or more branched C8 to C16 carboxylic acids;
• carbonating the mixture to form an overbased magnesium sulfonate;
• vacuum stripping the overbased magnesium sulfonate at about 160° C. to about 200° C.;
• and treating the vacuum stripped overbased magnesium sulfonate at about 160° C. to about 200° C. with 6 to about 10 weight percent of polyisobutylene succinic anhydride, wherein the polyisobutylene has a number average molecular weight of about 900 to about 1500 and having greater than 50 mol percent of terminal double bonds, to form the overbased magnesium sulfonate detergent;
• and
• (b) combining about 0.02 to about 5 weight percent of the overbased magnesium sulfonate detergent with up to about 0.4 of glycerol monooleate friction modifier;
• and
• wherein the combination of the overbased magnesium sulfonate detergent and the glycerol monooleate friction modifier is storage stable at about 55° C. for at least about 18 weeks.