The factory thermostat is supposed to open at 80C. Like all manufactured items, there is some tolerance in that number. You can easily test the thermostat by forcing it open and jamming a string in it. Then suspend the thermostat in a pan of water and heat it on the stove while watching a thermometer in the water. The temperature at which the thermostat drops off the string is the actual start-of-open temp for that thermostat.

100C will not hurt the car; up to 110 will be OK for iron-head engines such as the 61x family but I'd be cautious over 100C. Iron heads can crack too.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970