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iMac 20" Early 2008 Fan Speeds

As you can see from the photo, my CPU fan is running close to 4000rpm but all temps are fairly low. When I select any settings within iStat Menus, it does nothing at all for the CPU fan speed, but it will control the others as expected. I have done the SMC Reset, and pretty much every other "fix" I can find online. Anyone know what is going on? Sometimes the fans speed up as soon as I log in, and sometimes it'll be after about 5 mins. Also, this began before upgrading to Yosemite, it happened in Snow Leopard, Mavericks, and now Yosemite. Thanks!!

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iMac, OS X Yosemite (10.10.5)

Posted on Aug 31, 2015 10:51 PM

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2 replies

Aug 31, 2015 11:01 PM in response to austintg

You may have a hardware problem such as a bad sensor. Make an appointment at the Apple Retail Store - Genius Bar and take it in for service. If you are not in the USA or cannot set up an appointment this way, then contact your local Apple Store directly.


upekkha-AppleHardwareTest · GitHub

Intel-based Macs- Starting up into Apple Hardware Test

Apple Hardware Test- iMac (Mid 2007) and later models

Sep 8, 2015 9:46 PM in response to austintg

Took it to them and there were no relevant problems that showed up in diagnostics. All it showed was an issue with the power supply proximity "something or other" was messed up. Basically they said I would have to find a logic board and replace it myself. The computer runs great other than being annoying with the fan running so loudly. Oh well.

iMac 20" Early 2008 Fan Speeds

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