When I drove my '71 220D (4-sp) from Va to Id, I got 34-36mpg in level ground, 60mph interstate cruising. The car ran for 10 hours a day so it was completley up to temp for almost all of those miles.

Driving around here in hilly terrain in Id I average 30mpg, but my driving is 90% highway at 60mph where the car will hold that speed. There are a number of hills where all I can do is rest the throttle on the floor and see what she'll do.
By comparison, my Chrysler LeBaron averages about 26mpg cruising over the same route at 65-70mph depending on my mood.

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1971 220D/4-speed ~250K mi. Family owned (dads side) through three generations since <5K miles.
1992 Chrysler LeBaron, 3.0V6 125K. Family owned (moms side) through three generations since new.
1977 Chevy Camaro Continual hotrod project
1970 Cadillac Sedan DeVille 472ci and nearly 19' long
1974 Fiat Spider Still needs work