The viscosity index is a crucial metric, which can be used to assess the viscosity stability of an oil. Modern automotive engine oils are almost exclusively multigrade oils. The 5W part refers to the low-temperature viscosity or how the oil behaves in winter, 30 refers to the high-temperature viscosity (summer). Multigrade oils must fulfil two viscosity specifications, their viscosity grade consists of two numbers such as 5W-30, for example.
Kinematic viscosity meaning iso#
Under the ISO VG system, oils are generally separated into two main groups, multigrade oils and monograde oils. The resulting system is known as the International Standards Organization Viscosity Grade, ISO VG. A group of renowned standardisation institutes consisting of the International Standards Organization (ISO), American Society for Testing and Materials (ASTM), Society for Tribologists and Lubrication Engineers (STLE), British Standards Institute (BSI) and Deutsches Institute for Normung (DIN) created a common viscosity classification. In 1975 a common system of grading engine oils according to their viscosity was agreed. Low viscosity = fluid = fast flowing = less stable film High viscosity = viscous = slow flowing = more stable film In order to achieve a good flow of oil around the engine and good flow properties at low temperatures, the oil must be low-viscosity. The faster the oil flows around the engine, the better, i.e., the faster it can provide protection and prevent wear.
The time it takes for an oil to travel around an engine, especially at low temperatures, depends on the oil’s viscosity. How does viscosity affect engine oil selection? The technical definition of viscosity is the measure of a fluid’s internal flow resistance. Put simply, viscosity indicates how thick a fluid is and how easily it flows.
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