Much of the talk about oil revolves around the basestock (which does represent around 80%) but, modern oils contain so much more. Here are some of the addatives that can be present in that simple can of oil!

Anti-Ageing Additives (oxidation inhibitors)

At higher temperatures, oil molecules react with the oxygen in the air. In addition, metal surfaces act as catalysts to such reactions. The results of oil ageing are:

Increase in viscosity (oil thickening)
Formation of residues (coke, sludge, etc.)
Corrosion resulting from the acids formed

The inclusion of antioxidants in lubricant formulations can either avoid or retard these effects. Proven oxidation inhibitors are nitrogen, phosphorous and sulphur compounds (amines, phenols together with zinc, calcium, etc.).

Detergent and Dispersant Additives (dirt carriers)

The task of these additives is to hinder the coagulation of oil-insoluble residues such as resins and asphalt-based oxidation products and thus combat sludge deposits and oil thickening.
Moreover, these additives dissolve residues (cleaning effect) and neutralise acids. These additives can sometimes include succinimides, neutral metal sulpho-nates, phenolates, phosphates, thiophosphates, polymer detergents, amine compounds, sulphonates, highly molecular organic lime, lead and zinc salts, etc.

EP Additives (Extreme Pressure additives)

EP or anti-wear additives are used to increase load carrying capacity and reduce wear in boundary friction conditions (e.g. on cams, gear teeth, tappets, etc.). They work by forming metallic surface layers which prevent roughness peaks from welding together in boundary friction conditions and enabling metal surfaces to slide without wear by reducing friction.

The following agents are sometimes used:
zinc dialkyl dithiophosphate, tricresylphosphate,organic phosphates as well as sulphur and nitrogen compounds.

Viscosity Index Improvers (VI improvers)

These are substances (oil-soluble polymers) which improve the viscosity-temperature
behaviour of mineral oils, i.e. they reduce the influence of temperature on viscosity. At low temperatures, they improve flowing characteristics and at high temperatures, they increase viscosity.

Products used include polymethacrylates (PMA), olefincopolymers (OCP), polyisobuthylenes (PIB) and styrol-butadien-copolymers (SBC).

As VI improvers are very shear-sensitive, multigrade oils with wide viscosity ranges (i.e. 5W-40, 10W-40 etc.) should be formulated with unconventional base oils (e.g.hydrocracked oils, polyalphaolefins) which have much better natural VI characteristics.

Pour Point Depressants

Oils get increasingly viscous as their temperature falls until they cease to flow and start to solidify. This is caused by the crystallisation of paraffin molecules. The inclusion of additives such as polymethacrylate, alkyl-phenols, naphthaline with chlorinated paraffins, propylene-copolymers, etc. lowers the temperature at which solidification occurs.

Anti-Foaming Agents

Polysilicones (silicone polymerisates), polyethyleneglycol esters, etc. reduce foaming caused by churning. Excess foaming (air-oil mixtures) can result in inadequate lubrication. Seizures to bearings can occur if the oil pump draws oil-air foam instead of oil.

Friction Modifiers

These are surface-active substances which reduce frictional losses in boundary friction conditions and create defined frictional behaviour. This improves the efficiency of machinery. The substances used include fatty acids, fatty acid derivates, organic amines, amine-phosphates, etc.

Thats it.simple really!