The overheating went away at least for two twenty mile trips on hot day with a/c on. Temp was at about 85 degrees C all the way, both ways.
The misfire is at idle at low speed, at high speed, any time.
You say that the miss would show up in cylinder test, could it not be an injector, or something injection related? Is it your experience that injection system problems just don't cause a dead miss. I've never experienced a dead miss in a diesel, so I'm on unfamiliar ground in that regard.
I am still very concerned about the overheating, but it did temporarily go away.
Also the miss is so bad that it makes a resonant soft vibration at highway speed.
Thanks very much for your reply,
'84 Euro 240D, 523K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in