The Measurement of the Viscosity Stability of Multigrade Engine Oils and Its Effect on Performance

It is shown that the measurement of the viscosity stability of multigrade engine oils containing different VI improvers is dependent upon the shearing action of the test instrument. Mechanical rather than cavitational stresses must be used to obtain an accurate prediction of field performance. Car make as well as average engine speed influence the equilibrium viscosity of the used oil. The effect of shear stability on other performance characteristics of the multigrade oil are described in this paper.