CPU fan problem with 21" iMac 2010

Discussion in 'iMac' started by renderdeer, Feb 8, 2018.

  1. renderdeer macrumors newbie

    Oct 10, 2016
    I recently bought a used 21” iMac (2010 Dual Core i3 3,06GHz iMac11,2) online to replace one with a busted graphics card. After receiving the machine I noticed that the CPU fan goes full blast mid-boot and stays on all the time. iStat Pro showed that the skin temperature and the HDD proximity temperature sensors were not providing any data which I think is the reason for the misbehaving fan. All other temperatures were within sensible range (20-40 C).

    I’m now looking for advice on wether I should try and fix the sensors or just return the computer. I know the skin sensor is quite easily accessible if I can find a replacement, but I have no idea where the HDD proximity sensor is located - it is not the one inside the HDD, right? Or could there be some other cause I’m missing? The computer came with High Sierra pre-installed, I wonder if such an old computer is even properly supported by this OS.
  2. nambuccaheadsau, Feb 8, 2018
    Last edited: Feb 9, 2018

    nambuccaheadsau macrumors 68000


    Oct 19, 2007
    Nambucca Heads Australia
    Return it you are never going to be happy with it.

    Look for a later model with USB3, Thunderbolt and an inbuilt SSD. If the hard drive has been exchanged, it is necessary to fit a heat sensor kit to prevent fans doing just this. OWC for one have them.
  3. h9826790 macrumors G5


    Apr 3, 2014
    Hong Kong
    If you can get a full refund, and the seller never mention this behaviour. I personally also suggest you return the iMac and get another one.

    But if you can't return it for any reason. You may try MacsFanControl.


    AFAIK, that models iMac has a HDD fan. So, the SMC will command the max RPM if lack of HDD temperature sensor reading. This is normal.

    Since this fan is for HDD, even you force it to a lower RPM, it should be relatively safe because the CPU has its own fan. So, you may force this HDD fan to a lower fixed RPM that won't annoying you. Or you can make it base on some other parameters.

    But in any case, using MacsFanControl has risk. It override the system fan management, no matter which parts overheating, that HDD fan won't react to it anymore. So, please make sure you really know what you are doing. And make sure you leave all other fans in auto mode (especially the CPU fan).
  4. renderdeer thread starter macrumors newbie

    Oct 10, 2016
    Thank you for the comments, much appreciated. It seems the best course of action is to return the computer.

    The fault was not mentioned in the description, the seller even told me that this is typical symptom caused by dust moving around during shipping. Sounds quite dubious to me.

    I was also considering using MacsFanControl, but I don't think I could ever fully trust a third party software for thermal management. If I am for any reason unable to return the machine then maybe I will have to go this route.

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3 February 8, 2018