RTH,
You've gone through every thing in the cooling system itself. Now is the time to branch out to the other factors that might be causing excess heat. I think somone else pointed to the transmission as a possible source. I can say that I switched to mobil 1 ATF and noticed engine temps go down a few degrees. But I think you should really check injection timing before you go much further. Here is something I copied from the diesel mailing list On the bubble method.
Brian, Buy a used injection line from a junk... 'er, uh..
"recycler" and make you're own (nothing special about it -
just a short piece if fuel line bent into a "J" with a nut
on the end to attach it to the pump). OR use the Bob Sanigar
bubble method (that really is more precise).
> On the subject of diesel timing. If you are replacing the pump or rebuilding the engine. The simplest and most accurate way of setting the pump is: Disconnect the fuel line going into the pump from the filter. Take the spring and plunger out of #1 delivery valve, put the delivery valve back in and snug it down, hold the the pump linkage in the full open position. If you have the drip tube install it on the delivery valve, if not use the injector line in such a way that it is pointing away from the engine. It you don't mind the taste of diesel you can blow through the fuel line or use low air pressure. Put the open end of the injector line in a glass of water and watch the bubbles. Turn the engine slowly until the bubbles stop and check the timing mark. After tightening the pump recheck. This method is really more precise than it needs to be and although it may sound complicated it is very easy . Bob
--
August M. Booth, Jr. Ph.D.
Univ of Pittsburgh School of Medicine
"der Dieseling Doktor" mbooth+@pitt.edu
'87 300TD 143Kmi,'87 190D 2.5 193Kmi, '84 190D 2.2 217Kmi,
'85 190D 2.0 148Kmi, '87 190D 2.5 turbo 200+kmi, '84 190D
2.2 234Kmi dismantled
MBCA, GWSection
http://www.dhc.net/~pmhack/mercedes/mbooth1.htm
I hope this helps and inspires you to get to the real cause of your problem.
Bob D.
P.S. You did check for timing chain stretch last time you set your valve lash didn't you?