In the last 2 weeks sometimes when I close the lid on my MacBook 13" 2015 (OSX 10.12.6 3.1 GHz CPU, 16GB RAM), and put it away in my laptop bag, the machine continues to run.

I usually discover this a couple of hours later, when I go get something in my locker, and find my laptop bag emitting heat. The machine is hot to the touch, the CPU is throttling like mad, to the extent where everything slows down.

The fan needs like 10 minutes to kick in after the lid is open, and when I finally get “Activity Monitor” running, it shows kernel_task taking up huge amount of CPU.

Is there anyway to check which process is causing this?

p.s. checked Energy Settings. The following are checked:
* Put hard disks to sleep when possible
* Slightly dim the display while on battery power

  • This stinks. Please edit your question to add the OS version you are running. And obviously, what about your sleep/energy saver settings? – JakeGould Jan 15 '18 at 5:01

kernel_task helps keep processor temperature at safe levels. As the Macbook stayed on for a long time without refrigeration in the backpack it resorted to this function to preserve it.

Apple Support Link: https://support.apple.com/en-us/HT207359

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