I don't know if anyone remembers a thread on here where the question was asked if it was possible to go 600 miles on a tank in a stock w123 300D (turbo). But I've been trying for a the better part of the last 6 months to do it.
I did it!
Just barely, actually. I actually ran out on the exit ramp this morning on my commute. And yes, if you were wondering I had a jerrycan in the trunk with fuel just in case. I spent a total of 5 minutes on the side of the ramp (which was pretty wide as ramps go).
I haven't adjusted my car in any special way. My EGR has been blocked for years now. My tires are "stock", as is pretty much everything on the car. I usually get 26-27 mpg on most tanks. The only thing I've changed is my driving habits.
My commute is 24 miles one way. Several decent hills, mostly back country roads.