iMac just shutting down - overheating?

Discussion in 'iMac' started by imacken, Jan 16, 2018.

  1. imacken macrumors 65816

    Feb 28, 2010
    In the last couple of weeks, my late 2015 27" 395X 32Gb RAM 4GHz i7 iMac is just shutting down on me regularly.
    This happens in Windows bootcamp as well as macOS, and is always when I am playing demanding games, e.g. Deus Ex Mankind Divided, DCS, etc.
    I am vey concerned that this is due to overheating. See attached graph from iStat. Through the period of this graph, I was playing Deus Ex MD. The dips are where the iMac went to sleep!
    Any thoughts on this?
  2. SecuritySteve macrumors 6502a


    Jul 6, 2017
    You may have faulty hardware. Boot in diagnostic mode, and check if anything comes up. Thermal shutdowns shouldn't happen unless you're running intense computation in an already hot room.
  3. Mac32 Suspended

    Nov 20, 2010
    Are you overclocking the GPU? If the GPU draws too much power, the power supply will restart the computer (esp. when using modern dx11 games). Otherwise, I recommend using Mac Fan Control, and set a higher constant fan speed to avoid the temperatures going into the red. Afaik this particular GPU will run very hot, and you also have the hot i7 CPU.
  4. TC_GoldRush macrumors 6502


    Dec 6, 2017
    Nevada, USA
    Happened to my late 2015 iMac last year, would randomly shut down, even with nothing open! Apple sent me a replacement, same thing! Apple will just give you ****** refurbished hardware! Their computers are really going down the *******.
    What I'm trying to say is, it's not your fault. Apple computers nowadays are just unreliable blocks of metal that have a high failure rate. Ever walked into an Apply store? TONS of people having issues at the 'Loser' bar.
  5. imacken thread starter macrumors 65816

    Feb 28, 2010
    Thanks for that.
    @SecuritySteve The diagnostic test shows nothing.
    @Mac32 No I'm not overclocking.
    Surely temps of 105-109 over a sustained period cannot be right!
  6. SecuritySteve macrumors 6502a


    Jul 6, 2017
    Faulty hardware happens. Do you know how many times I did a custom build PC that had a fault in one component or another? It's a miracle that OEMs can produce pre-built products with a high success rate (Though not 100%). I don't think your issue is an Apple-specific issue, it's a computer issue. Blame manufacturers' QA process.
    --- Post Merged, Jan 16, 2018 ---
    Yeah that's not right. Have you considered bringing it in to an Apple store and seeing what they say? I mean it just strikes me as a hardware issue because you're having it in both Windows and macOS. Theres gotta be something going on here.
  7. imacken thread starter macrumors 65816

    Feb 28, 2010
    I know the 395X is designed for 105 degrees, but it seems to be going over this. Also, I don't think apps like SMCFanControl help, as there isn't an issue with fans. They kick in quite heavily with any 3rd party fan control when the GPU is being heavily loaded, and there is no problem with temps in normal (non gaming) use.
  8. TC_GoldRush macrumors 6502


    Dec 6, 2017
    Nevada, USA
    I had two replacements! Three iMacs with the same issue! They kept sending out faulty Macs which made me give up on apple! Their new iPhones are garbage too now! Once my 6s Plus dies, I'm done with apple.
  9. imacken thread starter macrumors 65816

    Feb 28, 2010
    OK, we get the idea! Enjoy Samsung and Microsoft. I hope they are more reliable for you.
    Personally, I love my iPhone X, and so do the rest of my family enjoy theirs. I have owned all iPhones since the 3, and I can safely say that the X is the best, and I have not had any problems with the hardware once.
    I have also owned several iMac, iPads and MBPs over quite a few years now, and this is the first time I have had any issue.
    Oh well, each to his own.
  10. h9826790, Jan 17, 2018
    Last edited: Jan 19, 2018

    h9826790 macrumors G5


    Apr 3, 2014
    Hong Kong
    High CPU / GPU temperature is normal on the iMac unfortunately. Is that right? There is no right or wrong, but Apple choose form factor over cooling, and Apple users love this path. However, it seems most iMac seems can survive for a reasonable period of time even Apple let the chips run right at their official limit temperature.

    So, is the temperature a problem? It may be somehow related, but hard to conclude that's the root cause of the shutdown. Since you mentioned it's 2015 machine, is your place dusty? Did you ever clear the dust? The GPU can survive at high temperature, but still need an effective cooling system to support. Pure thermal throttling cannot completely avoid thermal shutdown. So, if your cooling system is dusty, the temperature will be very hard to go down. Even thermal throttling can avoid sudden super high temperature, but the accumulated heat can still causing the GPU overheat (especially when the GPU under stress for a period of time)

    If you have compressed air / blower / duster... I suggest you can try to apply compressed air from the exhaust (of course, when the iMac is shut down), try to blow the duty out from the intake. I didn't own an iMac now, but this trick work for all my other electronics (PS4, XB1, Mac Pro, graphic cards, etc). Just apply compressed air back and forth few times. It can usually blow out most of the dust and recover most cooling ability. Of course, open it up is the best way to deep clean it. But I won't recommend any user to do that on an iMac unless they really know what they are doing.

    And since you said it happened in both OS. Then it effectively rule out software issue, but pointing to hardware issue.

    Of course, in worst case, the damage is already done. So, no matter what you do, the damaged GPU / CPU / VRAM (or the electronics around them) may still shutdown the Mac at anytime. Then you should bring it back to Apple, let them diagnosis, and fix it.
  11. webbga macrumors member


    Feb 22, 2014
    Cincinnati, Ohio
    My 2015 would lose the screen and go dark. Started happening about 9 months after I got the machine. Apple sent me to a 3rd party approved repair center and they replaced the Logic board. Everything was fine for two weeks and then the problem came up again. I took it to Apple and told them it was unlikely that two logic boards would fail in such a short time span without an external cause. They kept it a few days and replaced a faulty fan. Everything has been fine since then.
  12. joema2 macrumors 68000


    Sep 3, 2013
    I and several other users had this behavior on 2015 iMacs, and in each case the main logic board was failing and Apple replaced them. In my case it started out as a highly intermittent infrequent problem, but not only under CPU stress. Eventually (months after the problem slowly began) it could just be sitting there and reboot. The problems also showed up when the Genius Bar did overnight stress testing.

    After the logic board was replaced, my iMac was used for several years under multi-day high-CPU video transcoding, and it has not had another problem.

    Obviously your iMac should not shut down, no matter what you are running. There are various possible causes. I suggest taking it to the Genius Bar and having them run overnight bench tests.
  13. thefriendshipmachine macrumors regular

    Apr 14, 2017
    I had a similar issue to you maybe. I had a 2014 with the M295X. I noticed this blue stain on my screen and that the GPU would constantly run at 99C even with no games running, etc. I took my iMac in to get serviced because it had image retention (as is tradition, I wager most iMacs suffer from this) and the guy at the repair shop was like "oh btw we replaced the logic board, the fans, the heatsinks and the monitor. Your heatsink and GPU had an issue and burnt the device"... he also told me that my device was probably a "lemon" and that next time it broke I should ask Apple for a replacement (and of course he was right and it did break again - GPU failure - and apple replaced it with a 2017).

    I have the newest and also maxed out iMac, Macbook Pro, iPad Pro, iPhone X, Apple Watch 3rd series, AirPods:

    1. the iMac has been serviced 4 times for retention and heat and replaced once
    2. the macbook has been serviced once (it makes a crack/pop sound randomly) where they replaced metal/keyboard/trackpad/touchbar/battery and it still makes this crack/pop sound even after the repair
    3. the iPad Pro seems fine most of the time except on the boot screen there's this really weird artifacting going on
    4. the iPhone X seems fine
    5. the apple watch seems fine
    6. the airpods seem fine

    So 1 out of 6 devices totally flopped, 1 device is kind of cosmetically broken, but note that 100% of the apple computers I own have some sort of problem, and all my iOS devices are just fine. It never occurred to me before but maybe this is just yet another sign that Apple is slowly divorcing itself from the Mac and getting married to iOS.
  14. imacken thread starter macrumors 65816

    Feb 28, 2010
    Thanks for that. I haven't replied sooner as I wanted to test over a couple of days.
    So, I turned my iMac over, and blew out all the dust from the underside vent slots with compressed air, and so far, I have not had any repeat of the problem.
    Fans only come on while playing intensive, demanding games, e.g. Deus Ex MD, and go off very quickly after quitting games.
    Early days, but looking good so far!
  15. cynics macrumors G4

    Jan 8, 2012
    Can you log fan speed with GPU temp? Or at least compare manually?

    What is the max fan RPM you are seeing when temps are that high?

    Do you have any other software that would prevent the fan controlled via the system from reaching max RPM (~2700-2800RPM)?

    Is this a new problem? Have you always gamed like this? Anything changed? How dusty is the environment the iMac lives in?

    iMacs run HOT but thats spiking to 109c which seems excessive. Making sure the fan is acting right is the first step. If you need to open it to remove dust I would take the opportunity to reapply a very high quality thermal paste.

    When I used to game on my iMac I noticed the fan wasn't as responsive to GPU temp as it was CPU temp. I would set my fan to start speeding up toward max when GPU temp reached 90c just to prevent a wild spike but to never override the systems control for a high speed.
  16. imacken thread starter macrumors 65816

    Feb 28, 2010
    Max fan speed according to smcFanControl is 2300 and that is when the GPU is 100+.


    . I've always gamed like this, but the forcing into sleep is new.

    How did you do that?
  17. cynics, Jan 19, 2018
    Last edited: Jan 19, 2018

    cynics macrumors G4

    Jan 8, 2012
    I use a prog call TG Pro. It’s not a free app and in lieu of sounding like a shill you can set a trigger on any and/or multiple sensors to start increasing the fan speed at a certain temp. You can have it boost right up or gradual over time (so it’s no revving) which is what I did. The app would pretty much replace istat judging by its appearance.

    Screen Shot 2018-01-19 at 5.54.25 AM.png

    By leaving Main (fan) unchecked it will never override the systems fan control so there is no worry of it overheating. Basically it will use whichever is higher.

    However I would just find an app to set the fan to max (can istat do that already? if so use that), play dues ex for an extended period and see if the issue goes away. This way you can pinpoint the problem because as of now we are just assuming that is the issue.

    Surely MacOS logs this?! Someone more versed in the inner workings of MacOS has to know how to check this.
  18. imacken thread starter macrumors 65816

    Feb 28, 2010
    Looks interesting.
    Still, after a few days now, my problem is still resolved after clearing the vents with blasts of compressed air.
  19. ErikGrim macrumors 601


    Jun 20, 2003
    Brisbane, Australia
    I have the same issue with my iMac. Always used to happen with certain betas, so I chalked it up to bad thermal management. But it is happening right now again with 10.3.5 release so I decided to clean up the vents. Got a lot of dust out from the bottom air intakes with a wooden toothpick, so hopefully that should settle things.

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18 January 16, 2018