Society of Automotive Engineers (SAE) is a professional organization for mobility engineering professionals in aerospace, automotive and commercial vehicle industries. SAE is your one-stop resource for standards development, events, technical information and expertise used in designing, building, maintaining and operating self-propelled vehicles for use on land or sea, in air or space. The classification SAE 15W-40 informs us on the lubricant viscosity in two conditions, as follows: the oil has the viscosity 15 measured at low temperature (W – winter) and 40 measured at high temperature.
“W” next to 15 means cold (winter), that is why the first number refers to viscosity at low temperatures, and the second refers to viscosity at high temperatures.