I have a Touran 1.9 TDI PD 105, when I got it, on a run to work (40 miles down the A4) I could get up to 62 mpg indicated using the cruise control set at 60 (yes I slowed down in towns and generally stuck to the speed limit so I wasnt going overboard on the granny fashion driving).
Since then the 185/65/15's have been ditched for a good old set of TT copy's 225/40/18's. Doing the same trip has now brought it down to around 48 mpg and its still only got 20k on the clock.
Point is its not just the engine which is going to cost you in fuel but having said that a 150bhp re-map from Celtic tuning is planned next. £355 pound and they come to you.
Cant wait to get my Leon FR TDI in Yellow.....doesn't arrive till June.....whats that all about....they obviously don't understand the kind of torture in making people wait that long for a car.