As previously stated, a base oil must be refined to the highest level, and then compounded with specially selected chemical additives. The additives used depend on the specific application of the lubricant.
These chemicals are usually metallic based, and are designed to control deposits and keep engine components clean. They are able to clean existing deposits in the engine, as well as disperse insoluble matter into the oil. Detergents control contamination resulting from high temperature operation.
These are usually ash less organic chemicals, which control contamination from low temperature operation. Both detergents and dispersants attach themselves to contaminant particles, and hold them in suspension. The suspended particles are so finely divided that they pass harmlessly between mating surfaces and through oil filters. The contamination is removed from the engine when the oil is changed.
These agents reduce oxygen attack on the lubricating base oil.
Acids are produced by the combustion process, and when engine oil degrades with use. Unless rendered harmless by the engine oil, the acids can cause rapid deterioration of engine components. Corrosion inhibitors protect non-ferrous metals by coating them and forming a barrier between parts and their environment.
Rust inhibitors protect iron/steel from oxygen attack, by forming a protection screen over the surface of the metals.
ANTI WEAR AGENTS
These agents prevent wear due to seizure or rubbing surfaces. Compounds such a zinc dialkyt-dithiophosphate break-down microscopic hot spots and form a chemical filter which eliminates metal-to-metal contact.
VISCOSITY INDEX (VI) IMPROVERS
VI improvers control the viscosity of multi-grade oils. They are polymers which act like "popcorn". At low temperatures, they are "tight-balls" which do not significantly increase the oils resistance to flow. However, at high temperatures, these "tight balls" explode into long chain polymers, which interweave and increases the oil's resistance to flow (viscosity). The tendency of an oil to "thin" at high temperatures is controlled and reduced.
POUR POINT DEPRESSANTS
Base oils contain hydrocarbons that tend to crystallize into waxy material at low temperatures. Incorporation of a chemical which reduces the size of wax crystal formation can give an oil better low temperature fluidity.