ENGINE OIL ADDITIVES The American Petroleum Institute issues grades for engine oil that are shorthand for a certification that the particular kind of oil contains what is needed to protect a given kind of engine. These certifications are important because they ensure that the oil meets specific standards for performance and protection. It's a little known fact that common engine oils sold on the shelf already contain additives. These additives turn ordinary base oil into the kind of oil needed to provide the best protection for today's engines. To help, detergents, dispersants, anti-acids, friction modifiers and viscosity modifiers are always included in the additive packages that come standard with today's oil. And they all fulfill specific functions. Detergents keep metal surfaces clean by removing sludge contaminants. Dispersants work in conjunction with detergents to give the oil the ability to take particle impurities (like dirt or soot in the exhaust) and keep them suspended in the oil so they don't settle on engine parts.