We have only gone off the onboard computer, last month we drove from Belfast to cork mostly on motorways and it gave us 32.4mpg. I read on a ford forum that you should never trust the computers, ours has the 17” wheels and they reckon the computer calculates off the 16” standard wheels???
it think we just had a big shock coming from the fiesta where you would bang £20 in and it would last over a fortnight!
We really should do the full proper test and fill it right up then empty it and take note of mileage etc then fill it backup.
I might just go to the garages just to see what they will offer, I know were going to loose out a bit but you never know.
cheers