Magnesium is typically related to the detergent additive packages commonly used in engine oils. Detergents are used in lubricants to aid in control of deposits and help keep contaminants suspended in the oil so they can be carried to the filter and removed. In addition, some detergent chemistries also neutralize the acidic by-products of combustion. In doing so, they function as corrosion inhibitors.

In addition to the use of calcium sulfonates, magnesium sulfonates are used in engine oils as detergent additives. Although magnesium sulfonate is more expensive than calcium sulfonate, some formulators reportedly prefer its use due to what they feel is improved rust production seen with magnesium sulfonates as compared to calcium sulfonate in diesel engines. Because of this, whereas magnesium can be seen in the spectrographic analysis of diesel engine oils, today it is fairly uncommon to see it at any meaningful level in passenger car engine oil.

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