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  1. #1

    Member Since
    Jan 12, 2010
    Imac CPU Fan speed issue.

    I have a late 2008 Imac 24" - 2.8 GHz Intel Core 2 Duo / 2GB 800MHz DDR2 SDRAM. I am currently running OSX - 10.5.8.

    The problem i seem to be having is with my CPU fan. It seems to be running at full capacity whenever i run more than one application. The response time of the desktop doesn't seem to suffer at all its simply the buzz and whir of the fan that is annoying.

    I've have SMC fan control running on the system and the fan usually runs at a constant 3000 - 3500 RPM.

    I've done some research online and from what i've found is it could potentially be the heat sensor connected with the actual fan that is making the fan run at a higher rate of speed?

    At first i thought it might be SMC and maybe a corrupted file, but i've since removed and re-installed the program. I've tried resetting the fans (removing the power cable) and turning the system back on, this is a short fix that doesn't really solve any problems long term.

    My question to you is, apart from playing my music loudly to drown out the noise, what if anything can i do? Has anyone had this issue before? If so how did you fix it?

    I do not have an extended warranty with Apple.

    Any advice feedback or places to look for answers would be greatly appreciated.


  2. #2

    chscag's Avatar
    Member Since
    Jan 23, 2008
    Keller, Texas
    2017 27" iMac, 10.5" iPad Pro, iPhone 6s+, iPhone 7+, Numerous iPods, High Sierra
    It does sound like a wayward heat sensor. The normal operating fan speed (RPM) for your machine should be in the vicinity of around 1800 to 2000 RPM at idle. Of course as the load increases on the CPU or from HDD access, the fan speed will increase to keep the temperatures from rising.

    Your iMac is not easy to do any self work on as the entire display assembly must be removed in order to get at the inside of the machine. An iMac is actually built as a vertically standing notebook computer.

    You might want to visit iFixit: Apple Mac, MacBook, iPod, and iPhone Repair Parts and look at the step by step instructions for opening up your iMac and replacing components. There's no guaranty that it's the heat sensor, so keep that in mind.


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