I graphed my fuel consumption on the diesel for the last 2+ years. The average was 26.5 mpg. We live 13 miles from the nearest town so we do mostly highway 60 mph driving. It is slightly lower in the winter, probably warm-up time. Lots of variability due to foamy fill-ups with early shut-off. Max of 30 mpg - Min of 21 mpg. I just replaced the injectors and am hoping to due a little better over the next year.
83 300D, 238K miles
86 300TE Euro, 125K miles