I bought an 07 Diesel on friday and today has been the first time ive given it a decent run out. I put in £35 of Diesel today and it showed up that I had 360 miles until empty. I drove 50 miles sensibly on the motorway and noticed I still had 330 miles so from then I decided to keep an eye on it. I then noticed it had gone from 330 miles left to 340 miles. After 80 miles its ended up at 326 miles left so although ive done all them miles my indicator has worked out that ive only used 34 miles.

Does the diesel left on the computer sometimes rise like that? Im not complaining or anything but seems strange ive driven 80 miles but only used 34 miles in diesel.

The Range figure shown on the OBC after a fill-up is based on MPG of the previous tank. As you drive it can go up or down based on the MPG you're currently averaging.

Yes the range will increase if you're driving the car in a more gentle fashion, because you're using less fuel. Personally I think the OBC has the ability to revise the range based on your most recent driving (e.g. previous 5 minutes etc).

The range calculations are typically based on the last x miles of driving (I think the Fiat uses the last 30 miles) so it's very possible that if you drive it like you stole it, refuelled and then drove like Miss Daisy that the range would not go down as the miles piled on, or would actually increase.

Chris