Fan does not run at normal?

Servus!

Now that it gets warmer again, the temperature at my thick also goes high again at slow drive in the city out temperature 27 degrees, motor temperature exactly 100 degrees, but my fan doesn't make the effort to move. I know the Audi 100 that the fan starts at just under 100 degrees.But all 3 fan levels work.

Greetings Steffen