I just picked up an '86 Mack Midliner yesterday which has the Renault 5.5L intercooled turbo diesel (Renault started acquisition of Mack in the late 70's, then sold Mack to Volvo in the late 90's). It had a 26' box on it which the guy I bought it from kept for storage, so I'm going to bob the frame and make a rollback out of it with a knuckleboom crane. In any case, the thing runs great (long story but $23K truck I got for $500) and come to find out it gets in the upper teens on mileage. Not bad for the size! The multifuel M35A2 I recently traded for will be lucky to see anything over 12MPG, then again it's a 6X6 that's always engaged.

The real and true beauty of diesel is that if you had the inclination you can make your own fuel. Very simple, lots of options and about the greenest fuel out there besides the car powered by compressed air. Hydrogen could be a greener fuel, but only if it weren't so dirty to produce (which is what most are ignorant of).