I've been having an intermittent problem with my late 2013 27" iMac for more than a year now and it seems to be getting more frequent.

Basically, I could be doing anything on my iMac (or nothing at all!) and I suddenly hear the fans spin up to what sounds like max speed. When the fans spin up like this, the applications I am using (typically Chrome, but others too), will work for a little while, ~30 seconds, and then become unresponsive. I am not even able to restart the iMac from the Apple menu (it just doesn't respond). Eventually, I get the "rainbow circle" (beach ball?) mouse cursor and I can't do anything else other than move the mouse around. If I keep waiting, the screen goes black and if I wait a longer time the black screen gets a circle with a slash through it. What I normally do is just power cycle the iMac as soon as I hear the fans spin up and the applications become unresponsive. The system crashes this way usually at least once and often a few times per day if I use it a lot.

Here's what I've done so far to troubleshoot:

  • After power-cycling, I go into Console.App, and select "Crash Reports" on the sidebar, it is always empty. Is it correct to assume that this means it was not an application that crashed?

  • I've tried sifting through the logs looking near the time of the crash, and I don't notice anything obviously strange, basically just normal looking logs and then boot-up messages. The problem is there's A LOT of messages. I am looking for "grave" sounding messages, but I honestly don't know what, exactly, to look for. Is it possible there's no clues in the logs?

  • I've run Memtest86, it passes all four passes. No failures detected.

  • I've wiped the machine and re-installed the OS about 3 times. The problem persists. I am on Catalina now, but this has been happening even with the previous OS, Mojave.

  • I've tried not using some Applications that are long-running. I've tried switching from Chrome to firefox, and disabled dropbox. No change.

  • Fan RPM's and Die Temps appear normal. I do notice that when the system crashes, these no longer update. Could it be a thermal issue that happens so fast, the system crashes before the sensors log the problem? I am not doing anything super-taxing to the system. I have noticed at least one spike in CPU temperature before around the time of a crash, but I haven't been able to see that consistently.

  • I cleared out the /Library/Logs/DiagnosticReports directory, and used the machine normally until the next crash. After the crash, the directory had a bunch of files. None of them had a suspicious filename extension (eg .panic, .spin, .tailspin). Only one had a timestamp that was at at most a few minutes from when the crash happened: "Google Chrome Helper (Renderer)_2021-02-02-082350_MY-MACHINENAME.wakeups_resource.diag". Sadly, I don't have even the foggiest idea what this log file is trying to tell me. The central issue seems to be something about "wake-ups", here's part of it (I can upload the whole thing somewhere if someone thinks this has critical clues):

Date/Time:        2021-02-02 08:21:48 -0500
End time:         2021-02-02 08:23:50 -0500
OS Version:       Mac OS X 10.15.7 (Build 19H114)
Architecture:     x86_64h
Report Version:   29
Incident Identifier: 52354DFF-B2C8-497A-8421-369191E5D935

Data Source:      Microstackshots
Shared Cache:     0x7b5a000 57CFFC05-B33E-3B2A-9BBC-D3A0F410A70D

Command:          Google Chrome Helper (Renderer)
Path:             /Applications/Google Chrome.app/Contents/Frameworks/Google Chrome
Framework.framework/Versions/88.0.4324.96/Helpers/Google Chrome Helper
(Renderer).app/Contents/MacOS/Google Chrome Helper (Renderer)
Identifier:       com.google.Chrome.helper.renderer
Version:          88.0.4324.96 (4324.96)
PID:              18226
Event:            wakeups
Action taken:     none
Wakeups:          45001 wakeups over the last 122 seconds (370 wakeups per second average), exceeding limit of 150 wakeups per second
over 300 seconds
Wakeups limit:    45000
Limit duration:   300s
Wakeups caused:   45001
Wakeups duration: 122s
Duration:         121.77s
Duration Sampled: 87.46s
Steps:            21

Hardware model:   iMac14,2
Active cpus:      8

Fan speed:        1202 rpm
   admin@mt-iMac DiagnosticReports % kextstat | grep -v com.apple
   Index Refs Address            Size       Wired      Name (Version) UUID <Linked Against>
     160    3 0xffffff7f84180000 0xf2000    0xf2000    org.virtualbox.kext.VBoxDrv (6.1.18) 9C1C33DF-8061-30A2-9266-C9284816A6A2 <8 6 5 3 1>
     163    0 0xffffff7f84272000 0x8000     0x8000     org.virtualbox.kext.VBoxUSB (6.1.18) 51E577B4-43B6-359F-B817-9C63A69E7943 <162 160 59 8 6 5 3 1>
     164    0 0xffffff7f8427a000 0x5000     0x5000     org.virtualbox.kext.VBoxNetFlt (6.1.18) 96E530DE-E34D-3447-89A5-FCF6646AE47E <160 8 6 5 3 1>
     165    0 0xffffff7f8427f000 0x6000     0x6000     org.virtualbox.kext.VBoxNetAdp (6.1.18) 63EFABA5-3341-3BEB-B47A-AAFCDD7312A5 <160 6 5 1>
     173    0 0xffffff7f80fb6000 0x6000     0x6000     com.getdropbox.dropbox.kext (1.13.0) 4FFF485B-204E-3E48-BC54-C1D406AB9E75 <8 6 5 2 1>
admin@my-iMac DiagnosticReports %
  • No third party hardware was connected, just Apple keyboard + trackpad.

  • I will try running safemode for some days and see if these crashes still occur. I understand that will mean it's a hardware issue, but what component/sub-system?

  • Switching to safari as my browser has kept the machine stable for 3 days and counting. Still curious about the root cause.

What else can I try? I am comfortable with disassembly and swapping parts, and in fact, am thinking about an upgrade from fusion drive to ssd and increasing the RAM, but if the system is unstable, I am hesitant to spend the bucks on an upgrade unless I can also find/fix the root cause of these crashes.

Any other ideas?

Here's the system...

  Model Name:   iMac
  Model Identifier: iMac14,2
  Processor Name:   Quad-Core Intel Core i7
  Processor Speed:  3.5 GHz
  Number of Processors: 1
  Total Number of Cores:    4
  L2 Cache (per Core):  256 KB
  L3 Cache: 8 MB
  Hyper-Threading Technology:   Enabled
  Memory:   16 GB
  Boot ROM Version: 429.
  SMC Version (system): 2.15f7
  • What is the version of macOS you are using?
    – sfxedit
    Feb 2, 2021 at 23:27
  • @sfxedit, Currently Catalina, but this also happened with the previous one, Mavericks.
    – teego1967
    Feb 3, 2021 at 0:54

3 Answers 3

  1. Let’s skip Console.app and check the source. Open /Library/Logs/DiagnosticReports and order the contents by descending date. Check for any reports around the time of your crashes. You want to look fro files ending in file extension .panic, .spin or .tailspin. If you find any, please provide a way for us to view those files.
  2. I’d suggest scanning your filesystem for corruption (i.e. Disk Utility) though I expect it to turn out OK, given that this issue seems to survive full disk erases.
  3. Are there third-party kernel extensions that you have installed? Please provide a copy of the output of the Terminal command kextstat.
  4. Can you work for a while in Safe Boot Mode (booting with Shift held down) and see if the problem persists?
  5. Do you have any third-party devices attached? Can you run without them?


  1. Can you share the output of pmset -g log for the timespan between your most recent clean boot and the subsequent reboot after failure?
  2. Can you try reproducing this issue a few times and see if you consistently see the Chrome wakeups_resource.diag file in your logs around the time of hang? If so, please find a way to share the file (e.g. via PasteBin). Chrome may be indirectly responsible for an interrupt storm and we might be able to see that.
  3. After reproducing a few times, can you temporarily stop using Chrome completely and try living on Safari?
  4. If the hangs continue without Chrome ever running, can you try uninstalling Virtual Box and DropBox? (Make sure that kextstat doesn’t show them anymore.) Even though you are not running those apps, these kernel extensions start at boot and are always loaded into kernel memory so we have to remove them to eliminate the possibility that they’re involved in the failure sequence.
  5. Can you list the filenames of the new logs that appear in DiagnosticReports?

Re: your comment about safe mode:

I will try running safemode for some days and see if these crashes still occur. I understand that will mean it's a hardware issue, but what component/sub-system?

Actually, the overwhelming majority of unstable behavior these days is due to software (and occasionally firmware) bugs. Your symptoms don’t smell like hardware failure, particularly since you’ve tested both your HDD and your DRAM. There is very likely a software cause and fix for this.

  • Thanks, I will try those and update my question with the results.
    – teego1967
    Jan 31, 2021 at 13:29
  • Thanks! I did get a crash this morning while in safe mode. I left it in safe mode overnight and there was a logd .crash file in the DiagnosticReports dir. Not particularly enlightening. I will pastebin the suspicious logs and post links next time it crashes (will try your suggestions and try to keep my experiments as structured as possible!).
    – teego1967
    Feb 3, 2021 at 18:22
  • Any luck with the above debugging steps?
    – pion
    Feb 6, 2021 at 9:32
  • Yes! I've been running for three days now without a crash. I switched to safari and left everything else alone. Hopefully this is the fix, but disappointing that chrome and Firefox might be involved. I might try switching back to chrome and add extensions one-by-one. If it really is a browser issue, it's weird that it takes down the whole machine.
    – teego1967
    Feb 6, 2021 at 14:54
  • Yeah, an app taking down a machine is by definition a bug in the OS. Your pmset and wakeup resource logs can help us start to isolate the cause. Ideally we want to get enough detail (and figure out what a minimal reproducing case is) to file a good bug report with Apple.
    – pion
    Feb 6, 2021 at 19:33

This may not be a definite answer, but since I have a iMac (21.5-inch, Late 2013), I might as well post my observations.

The internal drive on this Mac is a 1 TB HDD. The Mac did not start significantly slowing down until I installed Mojave, This is also where APFS was first used. Upgrading to Catalina did not help much.

There have been posts here at Ask Different which after reading I came to the conclusion that if APFS is employed, then you need a SSD. Being that the Mac can not up upgraded beyond Catalina, I was not really willing to open the Mac. So I pursued adding an external SSD. There is really nothing out there for Thunderbolt that I did not consider prohibitively expensive. USB 3.1 gen 1 (which is USB 3 or 5 Gb/s) SDD drives have come down in price and have type A plugs. (Both the 21.5" and 27" late 2013 iMacs have USB 3 jacks.) I choose an Inland Professional 480GB SSD which cost 55 USD. However, the USB cable was to short, but I already had a longer spare. This significantly improved the performance of my iMac.

I can run Big Sur in a VirtualBox virtual machine with better performance than when I ran Catalina on the internal HDD. (Yes, it does seem odd that you can not run Big Sur on the actually iMac, but you can in a virtual machine without having to perform any special hacks or modifications.)

I have been using the new external SSD for a month and only had one occasion where the problem you described with the fan speeding up followed by the Mac hanging. This was when I was working on a solution to question for Ask Different and Big Sur hung. This caused VirtualBox to hang and eventually the entire iMac. Anyway, the problem was definitely caused by the VirtualBox application.

You say you tried Chrome and Firefox. You might consider Microsoft Edge.

One other concern is there does not seem to be any indication of trim support for the external USB SSD. This may result in the drive eventually slowing down, but so far there is no indication of this happening.

You seem willing to open your Mac and replace the existing fusion drive. I wonder if you could not keep the existing drive and just add a SSD. There is some indication that you could add a secondary SSD "Blade" drive. Being a PCIe connection, this should result in significantly better performance that the existing primary SATA fusion drive. See OWC website for more information and videos.


I've been following this thread and ones like it for a while because my late 2013 27" iMac does the same exact thing the OP describes. It's infuriating. I've done brand new clean installs without adding any other software and the hang will still eventually occur. I've ran Catalina both with and without the 2021 update and the hang still occurs. This led me to believe it must have been a hardware issue, so I bit the bullet and did a boot camp install of windows 10... I've ran it for several days now, doing various tasks without any hiccups or hangs. This tells me it's not a hardware thing (as people here had already deduced) but I thoght I'd just add my experience in support of that idea. Still would love to figure out the issue though. I have no desire to run windows, nor do I want to keep my fingers crossed that I won't need to restart a critical workflow all over again should my machine decide to go belly up at some random moment

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