Your problem could be caused from a bad temperature sensor that screws into the head or the wire connection could be bad. Its a blue and screws in the head. This will cause your fans not too come on since the engine is getting misinformation about the temperature.

__________________
1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)