that's the same exact thing happened to my 07 X5 3.0si last saturday (6/4/11). I have almost 55K miles on it. A loud whirling noise came up slowly upon starting the SAV and gets louder when you drive especially upon revving up to 3000 rpm. No control message or warnings came up. The whirling noise (and I agree it's from the aux fan) was so loud that even the car next to me in a traffic were looking at my SAV. I was on my way home when the control message showed "engine temp is high, drive moderately, etc." I stopped the car and turned it off for 20 minutes. I decided to continue driving (i still have 13 miles to go) and upon exiting the freeway (less than 2 miles from my house), the power was decreasing even with gas pedal pressed and the control message came up with "engine overheated, turned off vehicle, etc." So I did and waited for 15 minutes. I was able to start the car and reached home. The car sits in the garage for a day waiting for monday for a tow truck to bring it to my indy mechanic (an indy euro car specialist). Any ideas on the issues behind that continuously on fan making a loud, high speed sound?

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2007 BMW X5 3.0si Black Sapphire

2002 BMW 325i Titanium Silver