I've owned a '82 240D for over twenty years, it used to get 26 + MPG all the time and on more than a few long Desert trips returned 32 ~ 34 MPG's with the car fully loaded and AC on max.
It's a slushbox, I try not to exceed 60 ~ 65 MPH when out on the open highway .
Last year I rebuilt the engine, broke it in carefully,rebuilt injectors and injection pump, no smoke and runs great but can't seem to get over 25 MPG anymore, once in a while I get 23/24 MPG's out of a tank .
Bummer this .
I still love the car though
.