this is all very interesting, I have a #14 head and its been replaced when I bought the car due to the PO walking away from it when he learned the shop wanted $1400 to replace the head (they also lost the original head when some metal hawk stole it off the shop floor). I got it as a mechanics lien and put a used head on it (after a valve job etc.) since then I've put over 40K miles on it and the block now has 305K on it.
So far the #14 head is working fine but I have a later head available in case.
Before I took on the cooling system mods described I would install an electric fan, I've been thinking of that but have other projects always getting in the way.
Oh, and a comment on temp fluctuations.
My OM604 cooling has temp fluctuations that are hardly anything compared to the OM603 but oddly my M104 seems to have a lot of temp variations, the engines use almost the same block and I assume the cooling systems are similar but I haven't really examined them closely. The diesel runs cooler of course. I'd like to take on the M104 and install an electric fan before I work on the '87 diesel.
DDH

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!