An inferior base oil cannot be converted into a premium product simply by the inclusion of an additive. Using a poor-quality oil on a continuing basis and attempting to overcome its poor lubricating qualities with some special additive is illogical. It is better to determine the manufacturer's recommendation as to the minimum API service rating required and then regularly use a blended lubricant of a higher service classification than originally recommended, if an improvement in lubrication is the objective.

From "The Practical Handbook of Machinery Lubrication"