These additives are commonly employed to safeguard machine components from wear and metal loss under boundary lubrication conditions. As polar additives, they bond to frictional metal surfaces. When metal-to-metal contact occurs in mixed and boundary lubrication scenarios, they chemically react with the metal surfaces. Activated by the heat generated during contact, they create a film that reduces wear. Additionally, they protect the base oil from oxidation and shield the metal from corrosive acids. These additives are consumed as they perform their protective function, leading to increased adhesive wear damage once depleted. They are primarily phosphorus compounds, with zinc dialkyldithiophosphates being the most prevalent.

Rust and corrosion inhibitors are vital for protecting metal surfaces in industrial environments, where moisture, salt, and other corrosive elements can cause serious damage.

Detergents and dispersants play crucial roles in maintaining engine cleanliness. Detergents prevent deposits on hot metal parts and neutralize acids formed in the oil, while dispersants work alongside them to keep diesel engine soot particles, typically under 1 micron, finely dispersed in the oil, reducing clumping and potential damage.

Viscosity index improvers (VII), also known as viscosity modifiers or viscosity enhancers, are polymer additives that adjust the viscosity of fluids and lubricants across their entire operational temperature range.

The pour point is the lowest temperature at which a lubricant remains fluid. At low temperatures, wax crystals in mineral oils solidify (crystallize), hindering the oil's ability to flow smoothly. This is where pour point depressants come into play. They decrease the size of the wax crystals in the oil, enhancing its flowability even at sub-zero temperatures.

Anti-foaming agents, including silicone polymers and organic copolymers, lower surface tension to prevent foam formation in lubricants. By reducing the contact between oil and air, they can also help decrease oxidation risk. Only small amounts are used in oil formulations, as excessive quantities can lead to increased bubbling.

Oxidation is the process where oxygen in the air attacks the weakest components of base oil, occurring continuously but accelerating at higher temperatures and in the presence of water, wear metals, and other contaminants. This leads to the formation of acids, which cause corrosion, and sludge, which increases viscosity and creates surface deposits. Oxidation inhibitors, or anti-oxidants, are sacrificial additives that help prolong the oil's lifespan by delaying oxidation.