Previous 1 2 Next 16 Replies Latest reply: Jun 2, 2010 12:44 PM by ttdog
ttdog Level 1 (0 points)
I'm running a 24" iMac with 2.8 GHz and 4 GB SDRAM.
After installing Snow Leopard a few weeks ago, I noticed the back of the machine (upper left hand corner and below) is much hotter than it used to be. Heat is also noticeable while sitting in front of it, at the left hand side. I have no idea what the heat limits are, and not sure if this is even a problem, but it sure feels hot to the touch. I've even installed a fan behind the machine to try and cool it down.
Last but not least, when I use a solid color desktop background, on the left side of the screen, it looks like a phosphor burn in the screen.

Any information or advise is appreciated.

Thanks Much,
Tom --Mac addict since 1985, 7 machines in the house and this is the only one I've had issues with.

iMac 24" 2.8 GHz core duo, Mac OS X (10.5.5)
  • Dave Barnes Level 4 (2,975 points)
    1. Surf to and download iStat Pro.
    2. Donate some money to iSlayer.
    3. Install the widget.
    4. Tell us what your (Celsius) temperatures are as reported by iStat Pro.
  • jamesholden Level 3 (710 points)
    Firstly until you've posted the actual temperatures we can't tell whether it is a problem, but iMac's do get warm on the outer edge, the frame is part of it's thermal dissipation measures.

    The phosphor burn could just be the lighting 'unevenness' due to the backlights being around the edge of the screen.

    As for the extra fan behind, I would get rid of it as your essentially blowing the heat back at the machine.

    If you get temperatures of less than 80 degrees celsius or the equivalent, then don't worry about it.
  • Marcelo Maia Level 1 (0 points)
    Im having the same behavior here on an iMac 2.66 early 2008. After upgrade to SL, GPU (only) temps raised up to 80c, Diode is around 84c. This on basic tasks like surfing the web, reading emails etc.

    But the weird thing is, when i play lets say Call of Duty 4, GPU temps falls back like it was in Leopard (something between 65, 70c). When i quit the game, some minutes later, it raises up to 79c, 80c again.

    So 80, 85c are normal temperatures for GPU? And besides, is it not supposed to be the other way around? Temps raises when starting games?

    Already reseted SMC and PRAM. Is this something to worrie about?

    Thanks for any imputs.
  • jamesholden Level 3 (710 points)
    I wonder if it has something to do with OpenCL in Snow Leopard, since that essentially allows apps written for OpenCL to use surplus GPU power to assist the CPU in non-3D tasks.
  • Marcelo Maia Level 1 (0 points)
    In my case looks like i have solved by just vacuum cleaning both the hole on the back and on the bottom part. Temps seens stable at 69, 70c now.

  • ttdog Level 1 (0 points)
    Hi Marcelo,
    Good advise, but that was the first thing I tried.
    Still too hot to handle.
  • ttdog Level 1 (0 points)
    Thanks much for the advise. I ran iStat while 1) doing my normal processing, 2) in idle screensaver mode. I ran them in Fahrenheit vs Celsius and will redo and send the info to you.

    Thanks again for the help.

  • ttdog Level 1 (0 points)
    Hello again Dave,

    Here are the iStat Temp Data in Celsius:
    CPU: 51
    Airport Card: 70
    Ambeint: 30
    GPU: 67
    GPU Diode: 69
    GPU Heatsink: 65
    HD Bay: 58

    HD Fan: 1284 RPM
    CPU Fan: 1393 RPM

    Thanks for your help.
  • jamesholden Level 3 (710 points)
    Those temperatures look perfectly normal are well within safe operating limits.
  • ttdog Level 1 (0 points)
    Thanks James,
    That's good news. But what bothers me is that I cannot even touch the back of the unit due to the heat it puts out.
  • Dave Barnes Level 4 (2,975 points)
    Download and install either smcFanControl ( or Fan Control (

    Increase the minimum fan speeds by 300 rpm.
    Check the temps after a 1/2-hour.

    For example, my CPU fan is at 1800 rpm and the GPU diode temp is 62°C. And, I cannot hear the fans whilst sitting in my quiet basement.
  • ttdog Level 1 (0 points)
    Thanks Dave,
    I will give it a shot.
  • Christopher Damiani Level 2 (265 points)
    OpenCL is in Snow Leopard but there are no apps that take advantage of it yet. So OpenCL cannot be the culprit. It may have something to do with SL though as mine has been having hotter temps as well and I have an early 2008 imac.
  • myhighway Level 5 (7,270 points)
    +I noticed the back of the machine (upper left hand corner and below) is much hotter than it used to be.+
    +But what bothers me is that I cannot even touch the back of the unit due to the heat it puts out.+

    Your aluminum iMac may become hot, but will not "overheat" to the point of danger, or relative to its specifications. The heat you can feel is proof that its cooling system is more efficient and more sophisticated than the brute forced air cooling system of older white iMacs. To avoid defeating this design, users must prevent the iMac from being operated in direct sunlight, and from being physically enclosed.

    The aluminum iMac was designed to include its aluminum case (used as a heat sink) as part of the cooling system in an effort (appears successful) to limit the need for the internal fans to increase speed to exhaust hot air.

    As a part of the design, it was possible (and preferable) to slim down the case to enhance the aluminum's absorption of heat from internal components. Thus a lessening in volume of hot air needing to be exhausted quickly, resulting in smaller, quieter fans operating at slower average speeds. This means less dust and hair drawn into the system from the worktop.

    In my opinion the evolution has been hugely successful as my Mid 2007 model can do far more with a relatively lesser energy input than could my several previous plastic iMacs.

    With all past Macs I think users have noticed that software conflicts have caused processors to work harder, with a typical increase in heat generation. There is no reason to believe things will be different this time.

    Message was edited by: myhighway
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