do a test with full tank (fill until it stops by itself), drive empty etc, fill up at the very same pump until it shuts itself down again.... then calculate actual mileage, the 10£ method is not really very reliable....
i have as much as 100% fluctuation in my mpg! depending on where and how far i drive.....
http://www.spritmonitor.de/en/detail/502160.html shows you all my fuelling.. (well some of the fillups are not "real" as i have overfuelled, i.e. partly filled the expansion tank)...
if i only drive it short distance to work i get as low as 20mpg..... on long distances i get up to 45mpg
