Fuelly is a great way to track actual MPG if you don't want to do it manually. Interestingly my 8P DIS isn't too far off the actual, just 1mpg lower than what it is tank to tank. However when I fill up mine often says 330-350 miles remaining. Only ever see 220-260 out of it though so I wouldn't say going on miles remaining straight after fill up is the best way to work out the economy. Just my 2p.