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Solution: Mac CPU running wild – kernel_task eating up all CPU


I had a strange problem on my MacBook Pro Retina 15’ during the last 4-5 weeks…

My kernel_task would erratically start eating up all CPU cycles until the Macbook practically slowed down to a grinding halt.

This happened especially when I was heavily using VMWare Fusion or Video encoding and when I was working on my Thunderbolt display…


Searching the “Interwebs” I found hundreds of “magical remedies” for this problem which basically constitute the 101 of OSX problem solving:

  • Repair the disk
  • Login as Guest/ create new Account
  • Start in safe mode
  • Kill all “strange” processes with Activity Monitor and “kill” in Terminal later
  • Reset PVRAM
  • Replace some kexts for the Audio driver and IOPlatformPluginFamily
  • Unload all LaunchAgents
  • Did spindumps
  • Did a clean reinstall of OSX


But the problem came back after each attempt.
I was on the verge of believing that it might be a fried motherboard when I found the solution here!

It actually is pretty stupid:

  • I have my MBP hooked up under the Thunderbolt Display and stacked on top of another MBP
  • Summer did arrive and we go from -10C to 35C

So the thing got too hot and kernel_task starts consuming all CPU cycles to slow down a potentially rogue process to cool the system down.

Just “unstacking” it and letting it sit and “breathe” normally, after 2 minutes kernel_task went back to normal.

So if you have the kernel_task process run wild, first and foremost try to just let it cool down before loosing hours in narrowing down the problem.

Link: forums.macrumors.com

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