From this thread: http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic;f=21;t=000032
quote:Calcium and magnesium are both white-to-silvery-white metals that are "base" metals. Base metals attack acids and turn them into salts before they can cause corrosion. These Base metal detergents and dispersants are also responsible for establishing the primary TBN of a lubricant. Magnesium is a harder metal than calcium and can cause hard deposits on top rings and crowns of diesel engines. Magnesium additives in too high a concentration can also cause gelling of the oil. "Most" of today's modern oils have lowered the magnesium or dropped it completely in favor of newer non-organic detergents. Much depends on additive interactions as to how much magnesium is used. There are also different Magnesium sulfinate and phenate formulations, and the latest formulations present no problems. Like ZDDP, it still a low-cost cost and tried-and-true compound for most oils.
Detergents (Surface Protective Additive): metallo-organic compounds of sodium, calcium, magnesium, boron phenolates, phosphates and sulfonates such as alkylbenzene sulfonic acids, alkylphenol sulfides, alkylsalacyclic acids; Lift deposits from surfaces to keep them suspended. Dispersants (Surface Protective Additive): Alkylsuccinimides, alkylsuccinic esters (alkenyl succinimides); chemical reaction with sludge and varnish precursors to keep them acid neutralized and to keep them soluble. Detergent-dispersants often are the same chemical or come in compounds to accomplish the combined function(s).