This is to be expected of course but I think this is very encouraging, more so than I thought. I brimmed the tank at the local Shell garage the other day and the computer claimed 300 miles until empty, which I thought was fair enough because the car is new and still running in etc.

26 miles on the trip since filling up and it now claims 292 miles until empty. Keep underestimating at that rate please!

It's not underestimating the miles left alters with whether your mpg goes up or down as it increases the miles remaining increases

Does the same with me, never had higher than 420 miles on a tank, yet I get 550 most of the time.

It adjusts to your driving. My dad normally only does town driving, and gets about 500 miles to a tank. He took me to uni and back while mines at the mechanics and, after 20 miles of motorways, it was reading about 580.

I'm lucky to get 300 miles on a full tank in my Zetec 1.25