I believe the oil needs to meet a fuel efficency target vs a reference oil (typically a 15w-40), AND have a HTHS viscosity no less than 2.9 or 3.5 respectively. I assume the 12FE needs to achieve a higher fuel effiency.
fuel efficiency is at it's best in elastohydrodynamic region, if you can improve the fuel consumption in boundary lubrication regime, or reduce the time spent in that regime it's possible to get big efficiency gains.
fuel efficiency is at it's best in elastohydrodynamic region, if you can improve the fuel consumption in boundary lubrication regime, or reduce the time spent in that regime it's possible to get big efficiency gains.