All W204's with an M272 engine (2.5, 3.0, or 3.5) have an electronically assisted thermostat. The thermostat is a traditional wax pellet design with 2 chambers, but also has an electric heater element to allow the ECU to control the temperature within a desired range depending on outside temperature, engine load, etc.
The minimum operating temperature is 80C, and the maximum (according to WIS) is 100C, but I've never seen it go that high. In the winter, I find that my 09 tends to run at a minimum of 90C at all times (once fully warmed up, which can take a bit of time if you're doing all stop and go city driving in very cold weather). But in the summer, I find that the ECU allows the temperature to drop between 80-85C if you're out on the highway at higher speeds (140 km/h or ~88 mph).
My dad's 08 C300 tends to run a bit closer to 85C in both summer or winter, but does hit 90C and stay there if you're not driving it at constant high speeds (such as city operation). At 140 km/h, it will not go above 85C.
Different years and models of W204's must have very slightly different ECU programming.