High oil viscosity could also increase the engine temperature above operating mark, and lessen the engine's ability to start in colder temperatures. On the other hand, engine oil with too high a viscosity could also hurt the engine by causing the engine to increase its fluid friction that will reduce fuel economy. If the oil becomes too thin, it can fail to adequately separate metal components during operation and thus invite wear. Motor oil viscosity grades are based on a scale developed by the API (American Petroleum Institute) lubricant. We can measure viscosity by measuring the rate at which a metal ball falls. Viscosity is the resistance to flow of a fluid. Honey, syrup, motor oil, and other liquids that do not flow freely, like those shown in Figure 7.1.1, have higher viscosities. Water, gasoline, and other liquids that flow freely have a low viscosity. Too low oil viscosity could also result to leaking engine seals.įor instance, the you're driving briskly along the highway during summer, the intense heat your engine generates causes the oil to thin. The viscosity of a liquid is a measure of its resistance to flow. For example, metal-to-metal contact and wear in the engine is increased, as is oil consumption, which leads to the engine emitting harmful deposits and more frequent oil refills. This page focuses on how to define viscosity, the different types of viscosity, and the different types of liquids which show either Newtonian or non-Newtonian flow behavior. Lubricants with too low of a viscosity for your engine could cause various faults. It is the resistance which a fluid shows when being deformed. Viscosity correlations discussed in this page apply to Newtonian fluids. In laymans terms, low viscosity indicates that the oil is thin, while high viscosity means. Newtonian fluids Fluids that exhibit viscosity behavior independent of shear rate are described as being Newtonian fluids. It is sometimes expressed in terms of centistokes (cS or cSt) 1 stokes 100 centistokes 1 cm 2 s 1 0.0001 m 2 s 1. How it reacts to changes in temperature, pressure or speed determines how well the oil protects your vehicle, as defined by AMS Oil. A lubricants viscosity is defined by its resistance to flow. Kinematic viscosity has SI units of m 2 s 1.The physical unit for kinematic viscosity is the stokes (St), named after George Stokes. Viscosity is the most important property of a lubricant.
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