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 listed in letter-number format, like CI-4 and CJ-4. Your vehicle’s owners manual will list the class designation of oil that is recommended for your vehicle.
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 modern engines. In other words, they help oil fulfill its basic functions in the engines. What are the oil’s most important functions? You would think it’s all about reducing friction and wear – and you’d be mostly correct. But that’s not the only thing motor oil does, by any means. It protects metal surfaces from particulate wear, keeps acids under control, and even performs the essential function of keeping the engine cool by helping to dissipate heat away from engine surfaces.
To help, detergents, dispersants, anti-acids, friction modifiers and viscosity modifiers are always included in the additive packages that come standard with today’s oils. And they all fulfill specific roles in helping the oil provide the best protection possible.
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 engine) and suspend them in the oil film, away from metal surfaces, so they don’t cause damage. Anti-acids are a broad class of additives that neutralize the acids produced in the engine environment. Without them, these acids would cause corrosion and damage in the engine. Viscosity modifiers are used to help the engine oil maintain the best viscosity across the broadest range of temperatures and conditions that the oil is likely to face. And friction modifiers (like ZDDP) are added to improve the oil formula’s ability to cope with high pressure conditions.