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I have my MacBook Pro (Retina, 15-inch, Late 2013), 2.3GHz, i7, 16GB DDR3 Ram with macOS High Sierra version 10.13.3 connected to dual monitors LG. My laptop is connected to the charger, so I can close the lid and use just the 2 external monitors.

My issue comes gradually every time. First 20-30 min of usage seem normal, it works fine. After that the CPU goes crazy for some reason. The Activity Monitor shows kernal_task at over 500% CPU usage all the time. Which is not normal at all.

I don't know what's wrong or how to solve this issue. I never have this problem when I use my laptop when its not connected to external monitors. Ideas?

UPDATE: After a SMC reset, 50 min later, the same issue occurs. This is a screenshot of the temperature and the activity monitor:

enter image description here

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  • I also have a MBP 2020 plugged to an external monitor. The laptop being brand new, it cannot be a hardware problem. Here is what worked for me: turn off “Displays have separate Spaces” from System Preferences -> Mission Control.
    – marcvander
    Commented Jun 29, 2020 at 13:01

3 Answers 3

Reset to default
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Kernel_task running at an artificially elevated CPU level is the OS's method of forcing the fans to speed up to cool the machine; the side effect is to slow the machine down too, which aids the cooling process.

It can be sign of a hardware issue, but in the case of running 2 external monitors would probably be expected.

You can try resetting the SMC, just in case, but the symptom in itself isn't a sign there is anything wrong.

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  • Why would it only happen when it's connected to the dual monitors only though? I'm using the same laptop right now and it works perfectly fine. It's the same thing every time. It only happens when it's connected to the monitors and it's not happening right away, but gradually. It works for about 30 min and then it slows down because of that kernel_task. So, it makes no sense to be to be a hardware issue. If it was, it should be acting the same way when it's not connected to the dual monitor setup. But i'll try with SMC Reset and see if that changes anything.
    – Dani
    Commented Feb 17, 2018 at 15:57
  • The graphics card is working much harder. 3 external monitors & the machine would be unable to keep itself cool enough. If it was actually a temperature sensor issue, then the behaviour would be similar without the external monitors connected, which is why I'm assuming all is actually normal.
    – Tetsujin
    Commented Feb 17, 2018 at 15:58
  • But that was not the case. I've used the same laptop with the same 2 monitors for about 2 weeks before I bought my mac mini. It never worked that way. It was normal. Also, I close the lid and it's just the 2 monitors. I dont know if I have to mention this, but I have macs fan control app installed. Could it be it or something?
    – Dani
    Commented Feb 17, 2018 at 16:00
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    Rather than adding new information after I've typed my answer, you ought to have put it in your question to start with. Reset the SMC & see what happens.
    – Tetsujin
    Commented Feb 17, 2018 at 16:02
  • Did that, reconnected it to the dual setup and I'd have to wait about 30 min to see if it start acting the same way.
    – Dani
    Commented Feb 17, 2018 at 16:11
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It turned out it's Macs fan control app that I had installed. For some reason, it's not working properly. I turned it off when the kernal_task's CPU went crazy again and it all worked fine after that.

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  • From the FAQ: why do I have high CPU usage by kernel_task when using Macs Fan Control? Thermal issues are causing kernel task to preemptively use up CPU to prevent overheating. Try putting fan(s) back to auto and if it doesn't help, try to reset the SMC.
    – GeekUser
    Commented Feb 18, 2020 at 10:23
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From their FAQ: why do I have high CPU usage by kernel_task when using Macs Fan Control?

Thermal issues are causing kernel task to preemptively use up CPU to prevent overheating. Try putting fan(s) back to auto and if it doesn't help, try to reset the SMC.

Basically you override fans with this app incorrectly and the system is overheating.

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