I would not run an M117 without a thermostat -- the opening of the thermostat closes off the recirulation of coolant through the block, with without that closing flap, too much coolant will circulate through the block and not enough through the rad. This may in fact be the problem if you do not have a factory spec thermostat installed -- there is a flat disc on the "back" (hot) side that closes off the recirc passage. I found this out the hard was on my old Audi Fox -- took four thermostats, none of which would let the thing run at the proper temp, until I bought one at the dealer. Problem was obvious at once, as they didn't look the same at all.....

Most likely, if the bottom of the rad is always cool, is that there is inadequate coolant flow through the rad, either from a dead water pump or from a clogged rad. Either one will cause exactly your symptoms. Get the rad out and have it cleaned -- the radiator shop can test the flow for you, and that will tell you immediately if it is clogged. Once you ahve a good rad in place, make sure you have the correct thermostat (I like Behr, but any other OEM is fine, too -- just don't get one at Autozone!).

You also need to check ignition timing -- I believe it should be 7 degrees BTDC at cranking speed (static), 5 degrees ATDC with vac, about 5 degress BTDC without vac. You may want to advance a bit more, but not more than 5 degrees, and make sure the vac retard works properly before setting it.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!