Like I said its possible I've got a NAV that is spot on and got lucky. Didn't mean to accuse anyone of anything just wanted to point out that using one tank could give one erroneous results. I averaged over several tanks to determine my % and thats much more accurate than using one tank like the SG manual states.

Also... you probably know this but remember that if you are using full tanks as a comparison for MPG on tank/NAV that the NAV ONLY holds a certain amount of data. I put only 40 miles on mine and presumably the data buffer is long enough for that.... so it matches. But by the time the tank empties the buffer will have filled up, overflowed, and all the "early" data is lost and the NAV is only reporting the MPG for the END of the tank of gas, not the whole thing. Admitedly that would presuppose that if you are always 1-2MPG high then you'd always be getting higher MPG from the END of a tank than the start... I suppose it could be the weight of the fuel that would cause that but on a 4,000lb vehicle that seems supect.

As for the data buffer effect..thats what is believed to be the case here on GreenHybrid from the evidence thats been presented.. that the NAV has a limited buffer of data its working with and a running average, not all the data from the last reset.

Theres no reason it HAS to be that way but someone at Ford decided a running average of the latest data was more useful than the average since the last reset. Go figure.

 

Didn't mean my post to come off as a post-accusatory reply. I was simply making the statement that I've gotten a pretty consistent variance while trying to keep the pump and fill level constant.

Maybe I (and my wife) are subconsciously driving more conservatively at the end of the tank knowing the unpleasantness that is soon to follow...

 

Didn't want mine to be accusatory either... just posting observations. No harm done.