I just got back from a 600mi trip. My SD only got 21.5 mpg averaging about 75. When I got there, I noticed lots of black soot all over the back of my car. Is it running too rich? My mechanic tells me that I have excessive blow-by also. Another MB mechanic says that my leaky exhaust could be a problem. The car is also leaking oil horribly. Before I left for the trip i put in about a quart. When I got there (300mi) I checked the oil and again put in a quart. I havent checked it since I got back but it seems like its either leaking way too much or burning a little and leaking alot. I just had the valves adjusted and the valve cover gasket replaced. It seems that it leaks more oil than ever now. I already have oil seeping up the front of the valve cover gasket. I had to tighten the bolts on the valve cover 3 times to get the leaks to stop from the studs/bolts. I also bought the turbo oil return gasket, seals, and grommet. What other areas should i check. I have about 10 spots underneath the car that oil is coming from. I've degreased the engine but still can't tell where any of it is coming from since there are so many leaks. I know for a fact that the lower oil cooler hose is leaking at the cooler and possibly the other end. I also know that the oil return line is leaking badly. All in all i'm spending too much money on oil! :-)

*bump*
Help this guy out

I must be like a ghost on every forum I visit.

ok I'll take a stab at it, first if it leaks more now than before the valve adjustment, I'd make sure no vacuum lines are pinched under the valve cover. If you had to retighten it three times it may be cut in half by now.
Next fix the things you know are leaking it will make the others easier to find. As to using oil are you adding a quart to bring it up to the second mark? On my 617 it seems to use down to just above the lower mark and stays there, if I "top" it off it uses down the same spot and stops using. Black soot on the back of the car-- yes its a diesel, if you have leaks in the exhaust, combined with sustained highway speeds this would be normal, all the oil leaks will add to this. As to the mpg I cant really say what the norm for your car is, on my '85 300 turbo I was get about 23-24 after bumping up my tire pressure, adjusting the valves and fixing a dragging emergency brake and a stuck caliper, I'm up to 25-26.
also the 10 or spots you see on the floor could be from two or three leaks, it does blow around in there a bit Good Luck, James

My OM617 had a nasty leak behind oil filter housing, I replaced those gaskets, and the oil leaks stopped for a while. The only hard part about this repair is that space can be tight in places...