![]() Resource or energy conserving engine oils are lighter viscosity oils. Thick oils trade off fuel efficiency to achieve this as the engine has to work harder to move the oil around. Thicker oils make it easier to maintain oil pressure and reduce the tendency for oil consumption, particularly in worn engines, he notes. "The tried and true SAE 15W-40 conventional engine oils that many use has competition from lower viscosity grade oils that promote better fuel economy and other benefits." ![]() The reasons to switch to using lower viscosity, full synthetic or synthetic blend engine oils continue to build, says Dan Arcy, OEM technical manager for Shell Lubricants, one of the world's leaders in lubricants technology and innovation. These designations apply to oils intended for gasoline engines for light duty vehicles. Some motor oils may also contain a resource conserving or energy conserving rating from the International Lubricant Standardization and Approval Committee (ILSAC) - a joint effort of U.S. and international vehicle and engine manufacturers and the lubricant industry. When comparing viscosity numbers, a higher number will not flow as easily as a low number.Īn oil displaying the API certification mark and service symbol identify quality motor oils for gasoline- and diesel-powered vehicles that meet performance requirements set by U.S. The second number, "30," is the high temperature viscosity. The thinner the oil when cold, the quicker it moves around the engine and the faster it protects vital engine components. This number refers to the viscosity of the oil when the engine is cold, and indicates the oil's performance when the engine is starting up. The number in front of the "W" indicates the low temperature viscosity. Multigrade oils are formulated to give the oil the flexibility to lubricate effectively over a wider temperature range than monograde oils.īy way of example, with an SAE 10W-30 oil, the "W" stands for "winter" and indicates that the oil meets certain viscosity requirements for operation in low temperature. There are two common types of SAE classifications: monograde and multigrade.Ī monograde oil (also called single grade), such as SAE 30, is designed to be used within a defined temperature range. The higher the number, the thicker the oil. The SAE rating specifies the viscosity of an oil to flow at certain temperatures. Under the API classification system, oils designed for gasoline engines are designed by an "S." Oils appropriate for diesel engines are indicated by a "C." If too thin or thick, more friction and drag will be created, resulting in premature wear and failure.Įngine oils are classified and rated in order to establish quality levels and appropriate applications for those oils.įor automotive applications in the U.S., engine oils are generally classified by their API (American Petroleum Institute) and SAE (Society of Automotive Engineers) ratings. ![]() This, in turn, determines the ability of the oil film to keep the surfaces apart, the rate heat is generated by friction and the rate the oil flows between the surfaces to convey the heat away.Įngine oils are commonly referred to as "thick" - having a high viscosity, or "thin" - having a low viscosity.Īccording to oil manufacturers, an oil should have a viscosity at the operating temperature that is correct for maintaining a fluid film between the engine surfaces.Ĭhanges in an engine oil's viscosity can affect the oil's lubricating (protecting) ability. That creates heat, stress and wear.Įngine oil is used to reduce friction by creating a slick film between metal parts that lets them glide over one another.Īn oil's viscosity - a measure of its resistance to flow, along with the pressure and speed of movement, determines the thickness of the oil film between two moving surfaces. When metal surfaces come in contact, they grind together causing friction. The primary purpose of engine oil is to stop metal from touching metal.
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