Gary,

I haven't looked at the gal/hour fuel consumption of an idling FEH, but in my previous car it was about a half gallon per hour. If I divide that out to determine how much fuel you save in a 10 second FAS, it's .00138 gallons. Granted, at highway speeds the FEH isn't idling, so the fuel savings is surely more. But even if it's four times more it's still only .005 gallons per FAS. If you FAS twenty times per tank it's .1 gallons. For my recent average MPG that would give me a boost of about .2 MPG overall.

So when you say that FAS will make your MPG much better, you would probably need to FAS more often or for longer durations than what I've figured, right?

Best trip: 48.9 mpg over 17.9 miles (scangauge)
Best tank: 40.7 mpg over 606 miles (calculated)