Investigations on the Rheological Behaviour of Multigrade Engine Oils

In order to meet the viscosity requirements of multigrade engine oils, mineral and synthetic base oils of various viscosities and viscosity index improvers having various chemical compositions are used. As a consequence of both the viscosity-temperature behaviour of different base oils and the unique thickening effect of a given type of VI improver, the high- and low-temperature viscosity characteristics of a formulated oil are a function of the base-oil/VI-improver combination. The viscosity characteristics can be more or less optimized to meet the desired viscosity requirements. To provide acceptable rheological behaviour in practical formulations, it may be necessary to accept low-temperature performance that is less than optimum in order to achieve greater shear stability at a lower VI improver concentration.