The experience I have had on my '00 C230K is that the needle is always at or ever so slightly above the 80c line. It rises slightly in stop-and-go traffic with the A/C running.

If it's between 95 and 100c and you're at highway cruising speeds, that seems to me like it's high, and it shouldn't be that high.
But perhaps the M104 runs warmer than my M111 does - not sure. I had a 190E with the 2.6 M104, and I never experienced operating temperatures at those levels though.

A little warm for my comfort ....

-Michael

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+AMDG+
2005 W203
Running as fast as I can to stay behind!!