What are the Classes of Lubricating Oil?

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  • Written By: Patrick Roland
  • Edited By: A. Joseph
  • Last Modified Date: 04 November 2019
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Lubricating oil is to engines what blood is to the human body. Much like the different blood types found in different bodies, there are different classes of lubricating oil, each serving a distinct purpose. Synthetic and semi-synthetic oils are the most common classes of lubricating oil. Within each of these classes, the oils are broken down into further classes for commercial-grade classes and service-grade classes.

Motor oil and crude oil are not the same thing. It would be impossible to operate an engine or keep metallic joints greased properly using the thick black petroleum from the ground. Initially, motor oil and lubricating oils were made from a byproduct of the petroleum refinement process, but this proved too unreliable for most situations. For this reason, synthetic oils were developed to mimic oil's lubricating properties while eliminating its tendency to gum up and fail. With this invention, two distinct classes were born: synthetic oil and semi-synthetic oil.

Synthetic oil chemically alters the makeup of petroleum, primarily to improve its consistency. This class of lubricating oil can be counted on to keep moving parts safe during long usage spans. This class of oil is sought in extreme weather conditions because its chemical structure allows it to function reliably in cold or hot climates. One of the biggest users of purely synthetic oils is the airline industry, because engine turbines demand this class of oil.


A more common lubricating oil is the semi-synthetic class. Purely synthetic oils normally are quite expensive, but semi-synthetics are more affordable. This stems from its composition; it consists of as much as 70 percent mineral oil, and the remainder is synthetic oil. This oil provides excellent lubrication to moving parts, but it suffers from lower performance and reliability. These oils are found in more domestic products, such as the engines of lawnmowers or automobiles.

These two primary classes are further broken down by their usage. Oils given a C-class designation are considered a commercial lubricating oil. This refers to the engine's compression ignition, usually found in diesel motors, and is created to withstand the strain of commercial usage. S-class designated oils are reserved for service-class lubrication that is associated with automobiles and trucks that operate using gasoline engines. These classes are created by governmental boards in many nations, such as the American Petroleum Institute in the United States.


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