The closest I have is from the 1969 MB "Technical Data: Passenger Cars" for the 220D: 8.5L/100km @ 101.25 km/hr. Then is says 7.5-10.5L/100km at average cruising, whatever "average cruising" is. And for diesel fuel according to DIN 51 601.

For me the 8.5L/100km translates to 27.7mpg @ 62.9mph. My long term average (11yr) is slightly under 36mpg with mostly two lane highway cruising at 55-60mph. Original owner's long term average (20yr) was about 34mpg with mostly two lane highway cruising at 52-53mph, which is the sweet spot for this particular engine. Mechanical differences are Power Service DieselKleen fuel additive vs. ATF, Shell Rotella-T 15W-40 vs. Pennzoil 30W, and 34psi tires vs. 32 psi. Second owner (1yr) never did fuel the car! The three of us all came from trucking backgrounds.

Figure modern engine oils add 2-3 mpg, add another 2 mpg for conservative MB engineering data, and who knows what the effect of modern tires and fuel are.

In my opinion, a properly maintained vehicle is only half of the answer of your question of how to increase mileage. The other half is your driving habits. I'm sure a search on this web site will indicate as many opinions as people participating.

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daBenz - 1970 220D