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Piston ring wear, bearing wear and fuel consumption have been measured in European engines run under fully warmed-up conditions at steady speed and load. The engines were lubricated with motor oils which were formulated from a range of types and concentrations of VI improvers and base oil blends. The viscosities, viscosity/temperature relationships and viscosity/shear-rate characteristics of these formulations varied widely. The results for all the oils tested showed a poor correlation with their low shear-rate viscosities measured at 210°F or 150°C but a good correlation with their viscosities measured at shear rates of 105 to 106 sec-1.