I know this is an old thread, but I just got 34 mpg on two fill-ups in my 87 TD which I am happy to report. The driving was virtually all freeway miles through southern CA, no A/C, and I kept my speeds at 65-ish (when possible). For one of those tankfuls, I was stuck in traffic for a while, but I did my best to drive smoothly. When I first bought the car 6 months ago, I got 29 mpg doing the same drives. Since then bought new tires which are low rolling resistance Michelins (Energy Saver A/S). I used the same diesel fuel pumps and tried to refill the tank consistently. Also, I have checked my odometer against highway mile markers. On the old tires, it read quite high (so I corrected for that). On the new tires, my odometer reads just slightly low (so a correction is hardly needed). I also add 12 oz of Diesel Kleen per fill up (and I included that volume in my calcs). I honestly doubt that low rolling resistance tires got me 5 mpg at highway speeds, but I am glad that they seem to have helped.


I probably won't ever achieve this again because 65 mph feels very slow on a day-long drive, but I just wanted to run a little experiment this weekend and share the results.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).