| Abstract: | The rheological behaviour of several multigrade oils formulated with four different polymer-type viscosity index (VI) improvers was experimentally studied at different shear rates ranging from 1000S−1 to 35,000S1 and at both VI reference temperatures of 40°C and 100°C. The investigation was an attempt to assess the effect of each polymer addition on the viscosity-temperature relationship, as related to its chemical type and to the shear rate applied. It was found that the viscosity loss with increasing shear rate is greater for hydrocarbon polymer types than for methacrylate, especially at low temperatures. It was also found that the viscosity index is affected by the shear rate as well as by the type and concentration of polymer additive; its significance is thus linked with the condition under which it is determined and cannot be used as an absolute criterion for the appraisal of multigrade oil performance. |
