So, you replaced the radiator and the thermostat at the same time? Aaacckkk .... if you did, we all may have missed the opportunity to see which one was the problem ...
I had been "betting" it was the tstat since you noted earlier it had a replacement radiator in it.
Can you fill us in on this?
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg