If the engine lubricating oil of a truck has the SAE designation 15W-40, what type of oil is it?

Question

DentroTest · Accepted Answer

Oils with a double number separated by the letter "W" (for "Winter"), such as SAE 15W-40, are multigrade oils. They are designed to work over a wide range of temperatures: the first number (15W) indicates behavior and fluidity when cold, during a winter start, and the second (40) the viscosity when the engine is at operating temperature. A monograde oil, by contrast, has only one numerical value (for example, SAE 30 or SAE 40) and is suited to a specific temperature. Considering it equivalent to an SAE 25 has no technical basis, because viscosity values are not averaged in that way.

If the engine lubricating oil of a truck has the SAE designation 15W-40, what type of oil is it?

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