I would suspect your thermostat is not operating properly, probably stuck in the open position.
Your thermostat should start to open at 87C and fully open at 102C.
My experience and others on this site is that M104 engines tend to run at about 90 degrees.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".