I have a Macbook Pro Retina with the following hardware:

Model Name: MacBook Pro
Model Identifier:   MacBookPro11,1
Processor Name: Intel Core i5
Processor Speed:    2.4 GHz
Number of Processors:   1
Total Number of Cores:  2
L2 Cache (per Core):    256 KB
L3 Cache:   3 MB
Memory: 8 GB
Boot ROM Version:   MBP111.0138.B15

I recently updated to OS X El Capitan; I have had the same problem occur to me twice now and it's getting me mildly concerned.

I randomly have CPU usage spikes from kernel_task, the highest of which I have seen was 660% CPU. This is frankly an unacceptable and unnatural setting for my CPU (I typically have a total usage of about 2-3%). The highest I've screenshot is this:

enter image description here

The first time, I did not record what I had open. The next time, however, I was ready, and this is the exact list of what I had open:

  • Two YouTube video pages (using the processes Safari Networking with a max of about 44% CPU, typically stabilized at 8-10% and https://www.youtube.com, which got to around 51% CPU max, typically around 10-12%)
  • Messenger. Doubtful that this had an effect, but, hey, you never know.
  • Skype. This dude was running at a consistent 50% CPU usage.

It is worth noting that I had to close both YouTube windows to actually gain enough control of my computer to open Activity Monitor. None of the aforementioned processes were spiking, just kernel_task.

Also worth noting is my fans - the fans were on maximum, blowing cold air. Even though kernel_task was spinning at 660% CPU, there was no actual heat being produced, as far as I could see.

It's at this point where I force shut down the computer - I had about .5 frames per second (1 frame every 2 seconds, was looking at the clock) and was getting nowhere when it came to even attempting to fix it.

If there is a bug related to this that I have missed, or some wacky thing with OS X in general that I'm missing, please let me know, as this is extremely frustrating and more than a little disturbing.


You have classic symptoms that thermal issues are causing kernel task to preemptively use up CPU to prevent overheating. If you haven't reset the SMC, try that one time. If the System Management Controller is actually stuck, the response to changing thermal measurements might lag or leave blowers on higher than they should be.

The answers above all point to things you can do to measure swap, processes, etc... but focus on thermal sensors (hardware issue) or external temperature (environment) which you can cool artificially to remove the slow down that's designed to manage heat.

If you can't measure the case temperature accurately with an infrared thermometer, try software like https://bjango.com/mac/istatmenus/ to check on the individual temp sensors and correlate them with the "spikes in CPU usage" by kernel_task. Also, resetting the SMC one time might be worth your while. If it's stuck, the response to changing thermal measurements might lag or leave blowers on higher than they should be.

  • That doesn't seem to be the problem, though - the fans were blowing perfectly cool air out of the vents. Also, when testing with a Ubuntu 15.04 external boot, there were no spikes in fan usage or thermal readings. Are you suggesting that a) the thermometers are miscalculating or that b) there is a fault with fan responsiveness? Or something else entirely? – Addison Crump Oct 6 '15 at 22:14
  • @VTCAKAVSMoACE Yes - the cold air reinforces that the sensors are faulty in my estimation. It's possible the SMC is messed up, so try resetting that once. – bmike Oct 6 '15 at 22:19
  • I have reset the SMC and verified it (the LED changed, so, it definitely happened). If kernel_task goes all out of whack again within the next two days, I will let you know. Otherwise, I'll mark this as the answer. – Addison Crump Oct 6 '15 at 22:27
  • 2
    I can say with almost full certainty that resetting the SMC worked. I've pushed my computer to far limits of CPU to generate heat and it was totally fine, as well as normal usage. I'm gonna make a final edit to make this more accessible and easier to find and mark this as an answer. – Addison Crump Oct 8 '15 at 16:52
  • Resetting SMC worked for me. – Julian A. Sep 27 '16 at 21:13

Take a look at your fans ! For my Macbook Pro ( 2015 ) it wasn't a software problem. The Mac was completely unusable. I opened the Macbook dusted the fans with a toothbrush. I also cleaned the heatsink. After removing the heatsink, I found that the thermal paste was dry. I cleaned the old thermal paste and put some new paste, with care. Result: no more problems with kernel_task. The fans went from a steady speed of 6000 RPM to 2000 RPM (total silence).


My experience supports the theory that excessive CPU usage causes kernel_task to run high. In my case, it often happens when I have too many browser windows open or YouTube videos playing.

Closing windows or apps usually solves the problem.

Other ways to cool things down:

  • Higher fan speed. I use Macs Fan Control from CrystalIdea to manually raise my baseline fan speed to a constant 2500 rpm, or 3000 rpm if needed.

  • Using a cooling pad for your laptop.

  • Air conditioning! The outside temperature affects the computer's temperature as well.

EDIT: I previously said "overheating" instead of "excessive CPU usage." It's more accurate to say "predicted overheating based on current CPU and fan speed," since the Mac temperature control system takes those into account as well.

  • My computer was not hot when kernel_task was taking up massive CPU percentages, as mentioned in the question. :P It was actually blowing cold air. – Addison Crump May 31 '16 at 20:35
  • The temperature control system on Macs takes into account predicted overheating as well, based on current CPU usage. It launches preemptive strikes, so to speak. – jkdev May 31 '16 at 20:37
  • I'll edit my answer to change "overheating" to "excessive CPU usage." – jkdev May 31 '16 at 20:38

High temperature in a part of the chassis from charging together with peripherals plugged in can cause this issue, at least on a 2017 MBP. Simply moving the charging cable from the left to the right ports can be enough to cool the hotspot and resolve the problem. On a machine with MagSafe charging try unplugging peripherals from the left ports until the battery is full.

CPU usage has nothing to do with this, as a hot CPU is throttled by reducing its clockspeed not by scheduling no-op load.

See https://apple.stackexchange.com/a/363933/27135 for proof.


Here's something you can try:

  1. Reboot (you may have already done so)
  2. Reinstall OS X from the Recovery HD
  3. Delete caches by doing these commands in the Terminal rm -rf ~/Library/Caches
  4. Delete all Safari caches (since it seems as if Safari may be the cause)

Edit: it appears as if the answer by bmike is much more accurate.

  • I just installed it the other day. Will just removing the caches theoretically work? (no edits have been made to anything that El Capitan put in) – Addison Crump Oct 6 '15 at 22:04
  • Wait, sorry. I realize what you mean now. I'll remove the caches. This problem is not persistent, just occasionally (twice in three days) occurring, to clarify. – Addison Crump Oct 6 '15 at 22:07
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    None of these are root causes of kernel_task spiking. Deleting caches will actually make things worse as the system does CPU cycles to rebuild the cached data. – bmike Oct 6 '15 at 22:09
  • Yeah - I peeked in the Caches folder and I can definitely suggest not deleting that. That could really tear up some important things if you're not careful. Please note that in this answer. – Addison Crump Oct 6 '15 at 22:11
  • @VTCAKAVSMoACE deleting caches will not mess anything up. – At0mic Oct 6 '15 at 22:16

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