This is the straight story on viscosity grade. The “W” quantity in, for instance, a 15W-50 motor oil outlines the viscosity necessities of the oil when it’s chilly. Because of this a 15W-rated oil has to satisfy sure standards at chilly temperatures. Taking our 50-weight instance, a 15W-rated oil will move extra freely than a 20W-rated oil in comparison at chilly temperatures.