IMHO, 100 degrees is not hot for a 500E, or even a 300E or E320.
It is in the normal operating temperature of the engine.
At 100 degrees, the thermostat is not even in the fully open position, yet.
We owners of W124's freak out a lot about operating temperature because the temp gauge moves a lot.
Does everybody realize that in response to owners like us, Mercedes designed a buffer in the temp gauge of W210's so that the gauge stays at 95 degrees when the temp goes between 95 and 115 derees celsius?
After 115, the gauge starts to record actual temperature.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".