Technically you could get 45 mpg with your car IF you only drive downhill. With the two 240D cars I have, I get average around town 26 mpg with the automatic and 30 with the standard. On both cars when I first got them I pulled the tanks and cleaned them.

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1979 240D Caledonia Green/cream gone
1982 240D stick Ivory/Palimino
1999 E300D White/grey