When you pull over sometime, check the overflow lines on the injectors -- they are the black fabric covere ones. I have to replace mine every couple years, they cost a bunch (get the real stuff, don't use rubber vacuum line, it swells up!). You can dump an awful lot of fuel on the ground if these leak, as the extra fuel from the injector pump can drain out, too. My 220D gained about 8 mpg last time I changed mine!

The injectors will be wet and stink of diesel fuel if they are leaking, and they will be lose if really bad. Get new ones at a dealer or a real Mercedes shop -- the cost about $0.70 per inch. You need to push them on with a pair of needle nosed pliers, and don't forget the plug in the short one on the end. Pull the plug out and re-use it.

My brother's 87 300SDL gets about 28 mpg with the AC on at 75.

And buy your diesel at a truck stop -- the local gas station appears to be selling winter grade fuel. All three diesels (220D, 300SDL, and Volvo 740 turbodiesel) got lowsy milage and make huge amounts of smoke on it!

Peter