Only way to get a true reading for mpg is to...Fill tank to neck,Zero trip meter,Put some miles up(the more miles the more accurate the reading),When you refill take a note of the miles driven and the litres it took to refill to neck,............DEEP BREATH ! Now divide the litres used by 4.54 to get gallons and divide the miles between fills by this gallon figure .DONE! My car with a mix of town and motorway driving always averages 38mpg....and thats a fair mix of usual pottering round in traffic and plenty of hard acceleration when i feel like it.Drive like a priest and get 50mpg or use the torque of the diesel and enjoy it and get 38mpg (a very reasonable figure)