How to test if Auxiliary fan is bad?

[CharlieHustleX5]

Originally Posted by n2red

My point is.. (and I apologise for the wordiness...) on a properly maintained engine cooling system, the use, or requirement for, the aux fan to be needed to maintain engine cooling should not occur. No matter how how hot, gererally speaking, the outside temp is, the temp guage should hover right near the center of the dial. Use of the aux fan won't change this reading.

Exactly what I was trying to assure urcbmw8 when I replied to his question. The AUX fan will turn on if engine temps reach approx. 120 degrees celcius. But on a maintained cooling system, the AUX fan will have no role in controlling engine temperature.