ציטוט:
Before SAE came up with this scheme to classify oils by their viscosity in simple terms, which hopefully the motoring public could comprehend and easily understands, there was no simple way to tell how oil would behave in automotive engine when "hot".
Back then oils had no W rating, which stands for "Winter". Since cars were seldom driven in winter this was not a real problem. The roads were generally unpassable and vehicles usually not capable of starting when temperatures approached freezing.
Therefore the SAE viscosity rating was based on how quickly a specific quantity of motor oil flowed through a test ofrice when heated to operating temperature (100° C or 212° F).
SAE "W" grades were added in 1952 as it became apparent that engines could not be started in Cold Winter Climatic conditions with some SAE 30 oils. The "Winter" (W) performance was originally defined as viscosity at 0°F or -11.8°C.
The "SAE" then on the caps of glass oil bottles and later on the tops of paper oil cans, does not stand for any magic, it is simply the acronym for "Society of Automotive Engineers".
