Also, don't know where you're located, but in most cars, its unusual
for the aux electric fan to come on unless it's very hot outside and/or
the car is stationary or in slow moving traffic. Normally the regular
fan should provide adequate cooling. I had a problem once on my 300SD
and part of the circuit was turned on by the A/C being on and the
refrigerant temp at the radiator being over a certain temp. It was
controlled by a relay. There's probably another part to the circuit
that turns it on if the coolant gets too hot too.