One of the major tasks of motor oil is to neutralize acidic products formed in an engine cylinder. That is why it must have sufficient alkalinity, which ranges from 2-3 mg KOH/g for the oils used in gasoline engines, and up to 70-100 mg KOH/g for cylinder oils.
Engine operation involves a change in quality characteristics of motor oils due to oxidation processes. Special antioxidant additives are used to prevent these processes. They contribute to the preservation of detergency and dispersing property of motor oils for a long time, thus keeping the engine clean.
Corrosion is also quite a dangerous threat for motors. For its prevention, anticorrosion additives, which are not subject to water washout, are added to engine oils. They form special protective films that protect metal surfaces from corrosion.
Beside good viscosity, oil must also feature good lubricating properties that prevent various defects on parts surfaces and reduce their wear.
Different surfactants are often used as anti-wear additives. Under certain conditions they can come into contact with metal and form protective film on its surface. These films reduce the intensity of engine wear under unfavorable conditions (increased friction), and prevent occurrence of protruding burrs and adhesion under heavy loads.