"Today, more frequently the car owner finds one "W" Grade and one "non-W" Grade on the label such as SAE 10W-30 or 10W-40. These are called multi-graded or multi-vis oils. Oils so labeled will have the low temperature starting ability of the lowest "W" Grade on the label and will still protect the engine after it warms up with oil having the thickness of the "Non-W" Grade."

The whole article:
http://www.kendallmotoroil.com/techtips/form8470.html




[Modified by cspu, 4:57 PM 7/26/2002]