It is generally known by automotive technicians that motor oil is a necessity; but how many of those techs know what it actually is? Differences in formulations, even within the same brand, can be as broad as the motor oil type, or as specific as the additive package used.
In order to help regulate the formulations and performance of the many types of oil, the American Petroleum Institute generated a system of classification for base oil types. The majority of each bottle of motor oil originates from a base stock taken from one or more of five categories, or groups.
Group I base stock is the least refined base oil from crude oil; these are most often utilized in straight-weight, conventional motor oils.
Group II base stock is more refined than Group I to remove more impurities and improve its properties as a lubricant. Group II stock is often used when creating many of today’s multigrade conventional motor oils.
Group III base stock is refined to the point that it will perform at the levels of any other synthetic base stock and hence it is called a synthetic.
Group IV base stocks are PAOs (Polyalphaolefin) or historical synthetics.
Group V is essentially anything that will not fit into the previous four categories, such as esters and polyolesters.
While one or more of the base oil groups make up roughly 80-85% of the motor oil, the remaining percentage comes from a combination of additives. The additive package can be any specific mix of viscosity modifiers, anti-oxidants, anti-wear additives, dispersants or more; with each component responsible for at least one separate task.
The viscosity modifiers are used to help keep multigrade motor oil within the desired viscosity range as the motor oil heats up or cools down. Anti-oxidants are used in the motor oil to help the oil cope with the high temperature extremes inside the engine. The anti-wear additives assist in lubricating the moving components, and the dispersants keep the impurities in the engine oil in suspension so they can be safely removed by the oil filter before the oil travels to critical components of the motor. It is the delicate combination and mixture of each of these components in the additive package and the base oil selection that truly determine the quality of each lubricant poured.
Courtesy of Quaker State.
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