Automobile OEMs are looking for improving fuel economy[1,2] of their vehicles by reducing weight, rolling resistance and improving engine and transmission efficiency apart from the aerodynamic design. Fuel economy may be improved by using appropriate low viscosity [3] and use of friction reducers (FRs)[4,5] in the engine oils. The concept of high viscosity index [6] is being used for achieving right viscosity at required operating temperatures.
In this paper performance properties of High Viscosity Index engine oils have been compared with conventional VI engine oils. Efforts have been made to check the key differentiation in oil properties w.r.t. low temperature fluidity, high temperature high shear viscosity/deposits, friction behavior, oxidation performance in bench tribological /engine/chassis dyno tests which finally lead to oil performance assessment. Three candidates of SAE 0W-30 grade oil with ACEA C2/API SN credentials have been chosen using various viscosity modifiers. Impact of viscosity modifiers on cranking, pumping, high temperature high shear viscosity and Kurt Orbahn after shear viscosity have been studied. Bench tests such as SRV/MTM, Four Ball WSD, PDSC, JIS K2514 and TEOST tests are also included in the study. Selected candidates have been evaluated in Seq IV(Wear test) and in an equivalent test to Seq IIIG(High Temp Oxidation) engine test benches. Effect of FRs on fuel economy performance of best candidate has been studied in chassis dyno test on actual vehicle. Results show that Moly as friction modifier in gasoline engine oils has significant effect in reducing deposits, may be due to some synergy with additive package and base oil used. Work also shows that high viscosity index and use of FRs have significant contribution on fuel economy performance. The authors have plan to use this concept in further study of low viscosity engine oils.