iMac CPU running too hot

Discussion in 'iMac' started by phobos, Dec 13, 2013.

  1. phobos macrumors regular

    Feb 25, 2008
    Hello there
    A colleague has one of the newer 27" iMacs with Haswell (i7 3,4GHz) and the CPU seems to be running way too hot.
    When rendering the fans start to kick in (which I never heard before on the previous generation) and the CPU temp goes to 100Celsius.
    When I'm rendering on the previous gen I'm getting temperatures around 80 Celsius and the fan never kicks in.

    Any of you guys with the newer iMacs (late 2013) care to post some temperatures for the CPU?
  2. SaSaSushi macrumors 601


    Aug 8, 2007
    Takamatsu, Japan
    I haven't done any rendering on mine, but I have done some gaming and thus far I haven't managed to get it to peak above 70°C or so on any of the cores.

    It is idling with the CPU proximity sensor at 42°C presently.

    100°C sounds dangerously hot. I thought the overheat protection kicked in and auto shut down the system at around 90°C or so
  3. propower macrumors 6502a

    Jul 23, 2010
    Was your last imac an i5??

    What you report for an i7 (if your rendering uses all cores like handbrake) is normal. At about 50 to 70% total CPU load on a LAte 2013 i7 imac the CPU temp will be around 95degC and the fans will ramp up to keep it there.

    THe i5 runs significantly cooler. - disabling Hyperthrreading through xcode can reduce these temps a little.
  4. SaSaSushi macrumors 601


    Aug 8, 2007
    Takamatsu, Japan
    Wow, I'm guess I'm not pushing my i7 hard enough because I haven't gotten it close to that yet. I'll try some rendering.
  5. irnchriz macrumors 65816


    May 2, 2005
    What are your other temperatures like and also what is the ambient temperature and humidity where you use the Mac?
  6. jdblas69 macrumors regular

    Aug 15, 2012
    Don't have an iMac, but have a 2011 mac mini with an i7 and when I run handbrake the temp will push close to 100C and fans will kick in top speed to hold it below 100C. I have ran handbrake 48 hours straight no shutdowns or anything. If the temps do get abnormally high there are sensors to trigger a shutdown.

    I think a lot people get too worked up about temp readings.
  7. SaSaSushi macrumors 601


    Aug 8, 2007
    Takamatsu, Japan
    OK, did a little research and according to Intel's own spec sheets the official maximum operating temperature for the i7 is 105°C at which point it begins throttling.
  8. phobos thread starter macrumors regular

    Feb 25, 2008
    Thanks for the replies guys. It seems awfully hot especially when the previous generation i7 when rendering peaks at around 85 or something like that and the fan never turns on!
    With this machine it immediately gets to 100 when rendering and the fan kicks in. Having to hear the fan the whole time the machine is rendering can be annoying for sure.
    As you say it seems to be normal for this machine but it's still difficult to accept that!
  9. seveej, Dec 17, 2013
    Last edited: Dec 17, 2013

    seveej macrumors 6502a


    Dec 14, 2009
    Helsinki, Finland

    your CPU has built in protection, so it should not be able to get so hot that it fries itself. Also, my experience with previous i7 iMacs (late 2009) is that they:
    - get hot easily (mine used to peak at 96 c)
    - the fans do get worked up pretty easily.

    The high-end iMac is in my experience a problematic tradeoff - trying to offer high performance when needed and a basically noiseless machine when not. Resultingly, the design takes the machine pretty close to the edge of the (thermal) envelope...

    So, you might have a problem, or you might not.

    If you have a problem, it's most probably caused by bad thermal conductivity between CPU and heat sink (typically: too little or too much thermal compound).

    The best part is: you can test for this pretty well, especially if you have another similar machine to compare with. The thing is, that when CPU loading increases, and CPU temperatures go up, two things happen:
    1# the fans start spinning harder
    2# (and only if 1# does not fix it), the CPU starts throttling down in order to protect itself (Anandtech has some good articles about this). Resultingly, your computer will become slower until the temperature falls... This is a built-in safety feature and should not be happening in regular circumstances...

    So, to test:
    - open Activity monitor and it's CPU utilization window (Cmd-2)
    - get some software to track fan speeds and temps
    - Do a DVD-rip with handbrake

    What to watch for:
    - After the fans kick in, and the temperature plateaus, does the framerate in Handbrake fall? If it does, by how much does it fall (I'd consider any frame rate dip below 10% as normal)
    - (If possible) compare the thermal (and throttling behavior) with another similar machine. If your machine exhibits significantly more throttling, you most probably have a thermal compound-related problem. Contact apple.

    Hope this helps,
  10. phobos thread starter macrumors regular

    Feb 25, 2008
    Sorry for the long wait for a reply.
    We did a test render animation that ran an hour or two. The animation was basically a still that ran for a few hundred frames. An increase in render time would be a giveaway of the CPU being throttled.
    The good news is that 1) the CPU is not throttled in the 100c temperatures 2) the temperature never goes higher than 100
    The bad news is that 1) you hear the fan all the time 2) I wouldn't trust the machine running a render for days.
  11. quagmire macrumors 603


    Apr 19, 2004
    If you didn't hear the fan at 100 C temps, I would be worried.
  12. phobos thread starter macrumors regular

    Feb 25, 2008
    That's exactly the problem. The fan instantly kicks in and the CPU temps go up to 100c.
    Have you actually read the first post?
  13. propower macrumors 6502a

    Jul 23, 2010
    Rendering is brutal on CPU and can use 100%. An i5 imac might not ramp fans but every other one will.

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