2017 iMac Fan/Temps After Motherboard Replaced - Normal?

Discussion in 'iMac' started by Velin, Apr 14, 2018.

  1. Velin, Apr 14, 2018
    Last edited: Apr 14, 2018

    Velin macrumors 65816


    Jul 23, 2008
    Hearst Castle
    2017 5k 27" iMac running a 4.2GHz Intel i7, Radeon Pro 580 8GB, 8GB RAM, SSD.

    Just got this machine back from warranty repair, it's eight months old. Motherboard was blown, along with two RAM sticks (was at 16GB, now down to 8GB until I can get replacement RAM). Have a new motherboard. I just ran diagnostics (cold boot + D), no error log.

    Now that the machine is back, it's loud. Like way loud due to the fan cycling much more often, and faster. While playing just a Youtube video, look at these temps:


    Cores hitting 96+C while running a browser video? And the fan sometimes is cycling up to its 2700 rpm max, which rarely happened before the original board failed. And with the original motherboard, I rarely heard the fan cycling or blowing unless I was pushing it. But now, when I launch anything, the fan is cycling up to max RPMs and the CPUs are in the low-to-mid 90s C. If I drop the fan to 1500 rpm, the cores are hitting pretty close to 100 C when not doing much (i.e. Word and Firefox). And before getting the machine back today, I never monitored the fans, CPU temps, etc. Only reason I'm doing it now is because the damn thing sounds like a blowdryer.

    Does this sound normal? If I go back to the 16GB RAM, is that going to make a difference? I don't see how it could, because Activity Monitor says system idle is at 45%, so there is a lot of headroom. Then again, I'm not doing much, and Activity Monitor says "User: 52%" and "Sytem: 0.64%" I don't know if that's normal, either, just for being in a browser window.

    So, the machine doesn't sound right, doesn't look right. But, now I'm wondering whether the original board failed because the fan wasn't cooling enough. I know there are lots of reports about the i7 iMacs running hot, fan noise, etc. I never experienced these problems or issues with the original motherboard. But post-warranty-repair, I am now, after the motherboard replacement.

    So, anyone else with these kinds of issues?

    Another thought: would a SSD wipe and a clean OSX install make a difference? The SSD and data survived the motherboard failure, so I'm running off the original install. Do I need to do a clean install for a properly set up EFI with this new board? Could this be the culprit?

    (Yes, I hate the term "logic" board.)
  2. webbga macrumors member


    Feb 22, 2014
    Cincinnati, Ohio
    --- Post Merged, Apr 14, 2018 ---
    I bought a 27" at the end of 2016 and had the mother board replaced twice. The first time was after 9 months. The screen would go black while I was working, return after a minute, and then everything on the screen would be shaky. Apple Repair was backed up so they sent me to a 3rd party repair center. After the repair the board failed again two weeks later I called Apple again. This time I took it to the Apple Store and they replaced the mother board and a fan. I have not had the problem since. It is too much to believe that two mother boards would go bad that quickly. One. after nine months and the other a few weeks later. I would ask them to run diagnostics on the fan,

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