The demands on the automotive Industry to deliver improved fuel economy are long standing and continuing. A common and cost effective way to improve the fuel economy is to optimize the viscosity-temperature profile of a lubricating oil by employing a Viscosity Index Improver (VII). In this paper, we investigated the impact of the viscosity of engine lubricating oils on fuel economy and the influence of the VII in tuning the viscosity-temperature profile of the oil to maximize the fuel economy effect without compromising the protection under conditions of high temperature and high shear. We introduced novel comb type VIIs which have been specifically developed to provide the optimized viscosity-temperature profile required to give this balance. The way how these novel comb type VIIs were compared to more conventional VIIs in terms of the lubricating oil viscosity-temperature performance and also the resulting benefit in fuel economy are illustrated. We highlighted a recent study on a SAE 0W-16 oil, which is already of low viscosity, and further viscosity modification of what is already a quite efficient lubricating oil are less pronounced in terms of measurable influence on fuel economy.

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