Method of preparing an overbased or neutral detergent

A process for preparing an overbased detergent, the process comprising:

• reacting (a) a pre-prepared suspension comprising (i) a calcium or magnesium metal base with a mean particle size of about 1 micrometers or less, (ii) a surfactant comprising an ionic or non-ionic compound with a hydrophilic lipophilic balance of about 1 to about 18, and (iii) an organic medium comprising an oil of lubricating viscosity, a liquid fuel, a hydrocarbon solvent, or mixtures thereof, in which the metal base is suspended;
• wherein the metal base is suspended uniformly in the organic medium by a physical process and wherein the physical process results in the metal base having a mean particle size of less than about 1 micrometer;
• (b) an acidifying overbasing agent;
• and (c) an acidic or neutralised detergent substrate, to form an overbased detergent,
• wherein the physical process comprises milling, and
• wherein the amount of metal base present in the suspension ranges from about 40 wt % to about 65 wt % of the suspension.