What is an additive?

Additives are blended in with the base oil to extend or reinforce what the lubricant can do. They are a small share of the volume but they decide which specifications the oil can meet.

1. Viscosity index improverThe polymer coils when cold and swells when hot, so viscosity moves less with temperature. This is what makes a multigrade such as 5W-30 possible.
2. DispersantKeeps soot and low-temperature sludge suspended in the oil so it cannot clump together and build up inside the engine.
3. DetergentWorks at high temperature to stop deposits on pistons and rings, and neutralises combustion acids before they corrode metal.
4. AntioxidantSlows the reaction with oxygen that degrades oil into acids and sludge, extending its service life.
5. Rust inhibitorForms a film on metal that keeps water and oxygen away — important when a machine sits idle.
6. Anti-wearReacts with the metal to build a thin protective film that carries the load when the oil film thins, such as at start-up.
7. AntifoamBreaks up foam quickly — air bubbles interrupt the oil film and hurt heat transfer.
8. Friction modifierLowers the friction coefficient between sliding surfaces, which directly helps fuel economy.
9. Pour point depressantStops wax crystals from linking up in the cold so the oil still flows.

Every oil type needs a different additive package — which is exactly why using the wrong oil, such as engine oil in an automatic transmission, causes damage.