27" iMac Hard Drive Fan Problem


macrumors newbie
Original poster
Jun 25, 2010
I have a 27" iMac with 3.06ghz processor 1tb hdd and 4gb of ram purchased around march and I am having a weird problem with the hard drive fan. I brought it to the genius bar and they said the problem was with a program i was running(I dont believe them). I find the problem to be strange. I keep my computer running all the time and restart from time to time but rarely shut down. I noticed that the fan was running at high rpm's and they only solution was to shut down and restart would do nothing to resolve the problem. Then I noticed up in the next week that the same problem was happening. I started noticing a trend it was happening at the same time every week on the same day. I look up if there is anything in Activity Monitor causing the problem and I find nothing. Currently the only apps I have running mostly are Google Chrome, Mail, Adium, Itunes, Echofon and Dropbox. I wouldn't think that any of these apps are causing this problem. Anyone have any idea what could be causing this problem? Any help will be appreciated.


macrumors demi-god
Oct 9, 2005
Are you sure you didn't see anything in Activity Monitor occupying a high percentage of CPU time? Sounds like some app or process is getting stuck in a high activity loop, heating up the processor and causing the fans to kick on high. Even if the apps you list aren't the culprit, something could be doing it (printer daemon, Time Machine getting stuck... any number of things).

The fact that it happens weekly at the same time, as you said, makes me even more suspicious.

Fiddle with any Cron processes, anti-virus apps (not necessary anyway), or other command line/terminal settings? Install anything recently? Set any automated backups?


macrumors member
Mar 31, 2010
Atlanta, GA
Take a look here, this program will allow you to control your fans in your mac as well as show you the temps of the various drives. You can also go get iStat the widget and it will also tell you more temps than you probably wanted to know, along with activities going on, fan speeds, etc. It's a pretty useful little tool.



macrumors newbie
Oct 31, 2010
Same problem

I Have the same problem. after 3-5 days it the fan turns on and won't turn off. I have to reboot. I haven't added much software besides Open Office. Seems like a problem with the base machine/os.


macrumors newbie
Mar 29, 2011
Software to control iMac HDD Fan in relation to temperature

Hi, for anyone having issues with a overactive fan due to the HDD temp sensor not working, I have created a program that will let you set a fan speed to HDD S.M.A.R.T temperature relationship.

I made this as I was having the same issue having upgraded my HDD to a model that doesn't provide the correct temperature using the sensor cable.

I started using smcFanControl with sleepwatcher but didn't like the manual setup and the fact I was limiting the fan speed no matter the HDD temperature. now thats not a problem.

You can grab the software from


Its heavily based on Fan Control, but has been modified for use with the iMac and the HDD Fan, and now reads HDD temp using S.M.A.R.T. It also controls the speed OK with the overactive fans.

Hope this helps some of you. Let everyone and me know if it does.


Register on MacRumors! This sidebar will go away, and you'll see fewer ads.