4.9.8.a Viscosity of oils according to SAE classification
Below we will consider the designation of the viscosity of oils according to the SAE (Society of Automotive Engineers) classification.
This designation has two numbers that are separated by the letter W. This letter indicates that the oil is all-season. In this case, the first digit indicates the minimum negative temperature at which the engine crankshaft can be rotated. Thus, 0W40 oil should be pumped from –35 °С, 15W40 - from –20 °С. The second digit determines the viscosity of the oil at a temperature of 100 °C, or more precisely, not the viscosity itself, but the permissible range of its change. Thus, for "30" the viscosity at 100 °C can vary in the range from 9.3 to 12.5 cSt (centistokes are the units of viscosity measurement); for "40" - from 12.5 to 16.5 cSt, and for " 50 "- from 16.3 to 21.9 cSt. That is, the kinematic viscosity within the permissible range can vary by 10 ... 15%.
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