Oil Impacts on Sequence VIB Fuel Economy

The ASTM Sequence VIB is the new fuel economy standard for ILSAC GF-3. The new test pushes the bounds of current engine oil technology. With concerns over Corporate Average Fuel Economy (CAFE) targets, the auto manufacturers have been strong advocates of the Sequence VIB. This paper describes findings of some of fuel economy studies for GF-3.

The Sequence VIB is a significant step relative to the past Sequence VIA test in requirements for friction control. Stage-by-stage analysis indicates a shift to a higher degree of “mixed” lubrication response in the Sequence VIB relative to the Sequence VIA, 35 % versus 11 %, making both optimized friction modification and viscosity control necessary for obtaining high levels of fuel economy for GF-3. Viscometric contributions are controlled by both the (high temperature - high temperature) HTHS and basestock viscosity of the oil. Minimizing these viscometric measurements leads to improved fuel economy. Friction contributions are primarily dependent on friction modifier chemistry, although secondary impacts exist for detergent, dispersant, and zinc dialkyldithiophosphate (ZDDP).

The other significant change for the Sequence VIB relative to the Sequence VIA is the addition of a fuel economy retention measurement. Relationships are explored between used oil properties and fuel economy retention.