An Investigation Into the Effect of Viscosity Modifiers and Base Oils on ASTM Sequence Via Fuel Economy

The international Lubricant Standardization and Approval Committee (ILSAC) GF-2 specification requires Passenger Car Motor Oils to provide enhanced fuel economy in a modern low friction engine (ASTM Sequence VIA). In previous SAE publications the authors have studied the boundary lubrication regime and documented the impact of friction modifiers and antiwear additives on Sequence VIA fuel economy. This paper shifts the focus to the hydrodynamic lubrication regime and details fundamental studies of viscosity modifiers and base oils on fuel economy as measured by this low friction engine. The viscosity modifiers were found to have surprisingly little impact on this test, while moving to base oils of higher viscosity index improved fuel economy as might be theoretically expected. A study of formulating SAE 5W-30 motor oils with base oils of increasing viscosity index showed the optimum fuel economy was able to be obtained with a high viscosity index base stock.