Any thoughts on which conflicting numbers are right? Tank ave. MPG = 23.4. Trip Odo. = 400. Fuel added to fill = 15gal. (You know this is right.) Using these numbersthe old fashioned way gives me 26.66 MPG. By the way, the speedo with stock 18" wheels and Dunlop Maxxes is within .1MPH. I have a 350 w. 2,500 miles.

 

26.66 per galllon, of course. Four hundred miles on fifteen gallons

 

Probably added fuel, did you top off? Stop at first click? Every pump is probably different. You have to average it out over many tanks to get an accurate measurement.