"I would suggest that a two month long mileage check is much more realistic, so that the one underfilled tank that nets a wonderful 'mileage' number doesn't become the 'bragging rights number'"
I'm with you, Greg. There's no way to get realistic numbers on the short term.
Diesels are best as 'steady state' motors meaning that they're most economical at a single set low RPM. Driving a diesel vehicle makes steady state nearly impossible to achieve. But it's what we do, and in the doing there are some things that we can do to try to give the engine a chance to do what it does best. Driving slowly is a big help, but if that's not ganna' happen at least do everything possible to minimize throttle setting changes. Many people rely on cruise controls to do this even though the control, by it's nature, changes throttle settings almost continually. This actually can hurt milage. It would be better to use a dashboard control that can be set at a desired RPM and left alone allowing the torque built into the engine spec. to pull through small rises and downshifting for bigger ones. For downhills the braking systems, service, or compression, and to some extent gearing can hold back speed while changing RPM only to stop or move very slowly. Ideal, but impracticable while driving in traffic or, mountains and difficult for drivers used to gas engine techniques to do at any time.
Great theory and true but I just got back from a 2000 mile run towing 7000k one way and a little over 9000k on the way back in our '01 HO/6sp. Careful to be sure that my fillups were really full, and going 55 mph for most of the length of Calif. both ways (was ticketted for towing at 72 mph north of Redding on the way down and became scrupulously law abiding after that). The truck gave an overall of 19 mpg for the whole trip, and that's about the same as it gives when I hotrod empty around town.
You see, there's no figuring it out.
Attention: TDR Forum Junkies 
