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How are motor oils made and why do they work?

Motor oils are made from two main components, which are base fluids or basestocks, and additives.

Most of the oil, up to around 85% of the total, consists of base fluid, while the remainder is made up of chemical additives.


Base fluids may be synthetic or petroleum in nature. The petroleum fluids are the original basestocks that were used by the first motor vehicles and they are produced from crude oil that has been through a purification process.

Synthetic base fluids have been in common use since the ’70s and they are created in the laboratory by chemical engineering. As they have no contaminants, they do not need purifying.


The additives in motor oil are a package of chemicals that play an important role in ensuring the lubricant works as intended. Dispersants and detergents keep contaminants in suspension in the oil, so that they are not deposited as sludge on vital engine parts.

Anti-wear agents form a coating on metal surfaces, protecting them and extending their useful life. Viscosity index improvers are additives that help oils to maintain their viscosity over a wide temperature range, while antioxidants slow the oil oxidation process, helping to keep engines clean and free from sludge and deposits.

What does it do?

Once it has been added to an engine, motor oil works in several different ways to ensure efficient running. Perhaps most importantly, oil lubricates the engine’s parts, so that they can slide over one another without friction and power loss.

Oil also protects the engine from corrosion and wear, helping it to remain clean by preventing deposit build-ups.

Finally, motor oil helps to keep the engine cool because, as it flows through the system, it comes into contact with hot surfaces from which it carries away thermal energy. This heat is then transferred to the oil pan, from where it is lost to the air that surrounds it.

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