SAE (Society of Automotive Engineers) Viscosity Grade

The viscosity grade is usually the most prominent code on the front label. The viscosity grade is a measure of how the oil behaves under specific temperatures. In the past, the viscosity grade was a single number with higher numbers meaning thicker oils. In those bygone years it was absolutely essential to change oil with the changing seasons since thin oils, designed for winter use, would get too thin in the summer months to provide adequate lubrication. Today, through the use of viscosity index improvers, motor oil formulators have learned to design motor oils that work well regardless of the season. These modern oils are called multiviscosity (multigrade) oils and are labeled with two viscosity numbers. For example in a 5W-30 the first number is a reference to the apparent viscosity in cold temperatures and is further characterized by the"W" which represents "winter grade." The second number represents the apparent viscosity at high temperatures. Viscosity modifiers added to the oil allow it to flow freely at low temperatures and maintain adequate oil film thickness at high temperatures.