iMac Fans Running Constantly - How Can I Stop It?


macrumors P6
Original poster
Aug 17, 2007
Ok, so I just got my iMac back from having the logic board replaced. It booted up fine, but the fans are running constantly. They did not do this before the repair. Is there any way I can adjust this? My wonderfully silent iMac is now pretty loud.


macrumors 6502
Nov 10, 2009
one of the sensors are no plugged in I suspect.

Go and install istat nano and look at the Fan speeds and Temperature.

if you are missing one of the temp sensors then it is either unplugged or loose.

Should have a CPU, GPU, Optical drive, Hard drive, and ambient temp readings. if you are missing any of those then they forgot to plug something back in.


macrumors newbie
Dec 11, 2009
I have this problem too, which started during Migration Assistant. The noise was impressive -- louder than an Xbox 360 -- and continuous. iStat showed the HD fan spinning at 3400rpm, so it's going back to the reseller on Monday, and swapped out the same day.

Add another problem to the imac I7s! Fortunately, everything else seems okay.

My fan speed starts off silent (and does this if you put the machine to Sleep and then wake it up), but gradually gets louder over the course of 30 minutes.
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