LO 10-2 Describe the purpose, properties, function, composition, types, and applications of diesel engine lubricating oils

Lubricating Oil Properties and Oil Classification

Oil is commonly classified by its application, such as whether it is lubricating an engine or gears in a transmission or power divider or whether it is operating in a hydraulic system. Depending on its use, oil may be derived from biological sources, such as fish, vegetables, or animal fat. More often, lubricating oil, even synthetic oil, is primarily a product of petroleum refined from crude oil, also called mineral oil , which originates from the ground. Base stock is the term used for raw mineral oil processed from crude petroleum oil. It is interesting to point out that synthetic oil for lubricating engines is commonly made from selected molecules extracted from petroleum-based oil and are not artificially created. Polyalphaolefin (PAO) oil molecules, which are used to make synthetic engine lubricating oils, are chemically derived from petroleum and have the best characteristics of any hydrocarbon oil molecule used for lubrication compared to any other molecules found in mineral oils.

Conventional mineral oils contain a variety of different hydrocarbon molecules that have various sizes, shapes, and lubricating qualities. This means they will perform and respond differently to heat, pressure, bearing loads, and other engine operating factors. To be approved for the operating conditions and the unique engine technologies of various manufacturers, engine oils are refined and classified for use by the American Petroleum Institute (API) in North America and by the European Automobile Manufacturers (ACEA) in Europe. Before any engine oil is used, a technician must be certain that is has labeling or certification by the ACEA or API indicating its suitability for the types of technology affected by lubricating oil in a particular engine application. Given the variations of engine technology plus potentially different oil characteristics and qualities, the ACEA and API have developed a variety of specifications to define engine oil performance standards. For example, engines using high-speed turbochargers and recirculating exhaust gases into the combustion chamber place different demands on oil compared to lubricant demands in a naturally aspirated engine with little or no emissions controls. Length of drain intervals and the severity of operating conditions are some other factors that are important determinants for the selection of an appropriate lubricating oil.