rmmagow,

There was a recent post on this subject with a photo of the heater in the block attached. The location, as I recall is just a bit behind and above the front edge of the starter, on the passenger side of the block. If you have one, it will be obvious as there is a threaded plug with an electrical connection in the center that is readily distinguishable from a big hex plug. The unit is toward the rear of the block, at the same elevation as the other plugs along the side of the block (the others are not a hex headed plugs though). 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)