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. Blood viscosity is a major issue: blood that is too viscous can form dangerous internal clots, while blood that is too thin will not clot this can lead to dangerous blood loss and even death.The primary purpose of engine oil is to stop metal from touching metal. Viscosity can be of critical importance in medicine as fluids are introduced into the body intravenously. Lubricants that are too thin provide too little protection for moving parts. Lubricants that are too viscous can jam and clog pipelines. Manufacturing equipment requires appropriate lubrication to run smoothly. Some viscous fluids add texture to foods honey, for example, is quite viscous and can change the "mouth feel" of a dish. A thick potato and leek soup, for example, when it is less viscous, becomes French vichyssoise. Different cuisines also rely on the viscosity of sauces, soups, and stews. Fats, which are moderately viscous when heated, become solid when chilled. ![]() ![]() Cooking oils may or may not change viscosity as they heat, while many become much more viscous as they cool. Viscosity plays a significant role in the preparation and serving of food. Some oils have a more stable viscosity, while others react to heat or cold if your oil's viscosity index is low, it may become thinner as it heats, which can cause problems as you operate your car on a hot summer's day. In addition, viscosity also affects the rate of oil consumption and the ease with which your vehicle will start in hot or cold conditions. That's because viscosity affects friction, and friction, in turn, affects heat. When you put oil into your car or truck, you should be aware of its viscosity.
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