iMac "CPU A" temp 88C, fan constantly coming on

Discussion in 'iMac' started by rfs, Sep 3, 2009.

  1. rfs macrumors newbie

    Jun 18, 2009
    I have an 24" iMac8,1, running 10.5.8, and I've been having issues with the video card (nVidia 8800gs) for the past few months. I had the card replaced, but continued to have issues, and so last week I had both the logic board and the video card replaced (thanks applecare!).

    Since then, I've been noticing that the fan comes on a LOT. Pretty much any time I play a game, or even when I'm copying a large file to a network drive.

    Running the iStatPro dashboard widget, I see that there are two "CPU A" entries, and the second one is often going up over 80 degrees C. Even when it gets above 50C, though, the fan comes on and starts churning at about 3500 RPM for a while. Even when CPU A goes back to ~40C, the fan still stays on for a while.

    This whole time, the *other* "CPU A" temperature is around 40C. I'm not sure if these refer to the two CPU cores - if so, why would only one of them be getting hot?

    Anyway, I wanted to see if this behavior was at all normal, or if I need to call Apple again.

  2. J the Ninja macrumors 68000

    Jul 14, 2008
    A computer's CPU fan spinning up during a game is normal, especially for a slim machine like an iMac. The other sensor is likely a heatsink sensor or something, and will read lower. In any case, it seems like your iMac's cooling system is functioning as designed. Don't worry about it.
  3. indg macrumors 6502

    Feb 7, 2007
    i think you might be misreading the istat display. unless there are two physical cpu's (not one cpu with dual cores), there should only be 1 cpu reading, and maybe a Heatsink A and Heatsink B.

    80C is fairly high and would spin up the fans close to their max. heat probably damaged your previous logic board/video because the fans weren't running properly, and now you notice them because they are. just a theory.
  4. fhall1 macrumors 68040


    Dec 18, 2007
    (Central) NY State of mind
    88C for a CPU is pretty high...mine usually stays in the 40's when under load.
  5. rfs thread starter macrumors newbie

    Jun 18, 2009
    Thanks for the replies. indg - that is actually something I've been wondering as well. What I was hoping for was confirmation that other people with this model of iMac sometimes also get a) fairly high CPU temperature readings and b) 3000+ RPM CPU FAN readings, even when the temperatures are quite low.

    I should have been clearer on that second point - sometimes my fan ramps up over 3000 RPM even when I'm not gaming or really doing anything out of the ordinary.

    I am attaching a picture of what iStatPro is showing. This is right after rebooting the machine. Note that both "CPU A" temperatures are pretty low, but the fan is still running over 3000 RPM.

    It's that second "CPU A" temperature that gets up over 80 degrees sometimes...the first one always stays around 40.

    Thanks again for the help.

    Attached Files:

  6. mazza macrumors newbie

    Feb 23, 2008
    Imac Runs Really HOT

    My relatively new Imac (April 2009, 24 in OS 10.5.8) runs really HOT. Istat pro lists hard drive at 54, CPU temp at 44, heat sink at 43 right after bootup. Neither fan is running over 1200 RPM. Temps just keep climbing till you can't even touch the top. DVD's are ejected and feel like TOAST. Apple says there is nothing wrong. Still under warantee, but my even newer Imac at work does the same thing ? Do they all have this problem ? What should I do ?

    Attached Files:

  7. rfs thread starter macrumors newbie

    Jun 18, 2009
    For what it's worth: After talking to Apple about the issues I was having, and given my history of recent repairs (two new video cards and a new logic board in the last two months), Apple decided to just replace my machine with a new one. It's on its way now. I love AppleCare.

Share This Page