The Effect of Lubricant Viscosity and Composition on Engine Friction and Bearing Wear. II

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Abstract
In an earlier paper it was shown that mineral oils containing high molecular weight polymer would give better lubrication characteristics (lower friction and lower wear in a V-8 automotive engine) than straight mineral oils of the same viscosity. In this paper, the effects of polymer type, molecular weight and concentration are considered. Generally, friction and wear decrease with polymer concentration, leveling off to a “plateau” which is a characteristic of the given polymer. The level depends on both polymer type and molecular weight, the best results being obtained with the lowest molecular weight polymer. The behavior of polymer/oil blends is also sensitive to the presence of polar surfactants. It is concluded that both the bulk properties of oils, such as viscoelasticity, and surface effects are important in accounting for the advantage of polymer-modified oils.