Just a question about the chemistry. Having just returned from our annual 3,000 mile trek to the deep south (Ottawa - Florida return) I have been reviewing my mileage figures and discovered that somewhere I seem to have lost about 2 MPG on average. The two previous trips with this combination (6.2 na in a Buick Roadmaster with a 3,000lb camper out back) I got a consistant 28 MPG (IMP gal) throughout the trip. This time it worked out to 25-26 MPG.

This is the first time I have done the trip exclusively on ULSD. When they strip out the sulphur more then likely all of the other aromatics come with it. Is it possible these components added BTUs to the fuel? Up here in Canada we have yet to see ULSD on a consistant basis (or at least they are not advertising it) and this is the first time I could be sure I was using it. The car ran like a champ and I did use Power Service additive except for a couple of tanks of B5 but I can't seem to account for the drop in mileage.

Has anyone else noticed a similar difference?

Bill