turbodiesel,

The block drain is usually on the passenger side of the block, near the center (looking from front to back) or a little forward of center. I believe it is a 19 mm hex head bolt just screwed into a small boss on the block. On a 240D it is right next to the bracket that supports the front of the starter. It is in a similar spot on my 190E 2.3-16 although the starter is in another location.

If you are going to drain the block, you should use the garden hose method to rinse the old stuff out, and you should open the drain at the bottom of the radiator to get the most solid stuff out the shortest path. I would also recommend getting the MB citric acid powder to flush the system, which means another drain and flush cycle. I use the MB antifreeze exclusively, and it is clear, not orange (and has been clear for ten or more years now). I do add Redline water wetter, which makes the whole concoction pink, but also helps identify coolant leaks if you get them (a more apparent pinkish residue builds up at the leak). Good luck and I hope this helps, Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)