Fan running and mac slow and kernel task using lots of CPU%

Hi jojouu63,

It sounds like your Mac is running slowly. Identifying when this happens can be helpful. Is it when you are preforming a certain task or when using a particular app? Here are some isolation steps and resources that may help.

1. Review If your Mac runs slowly

• If it's isolated to an app review If an app freezes or quits unexpectedly on Mac.
• For more information on Activity Monitor, see Activity Monitor User Guide.

2. Test in safe mode as it can help you determine whether issues you’re experiencing are caused by software that loads as your Mac starts up. How to use safe mode on your Mac.

• As it also " It also does a basic check of your startup disk, similar to using First Aid in Disk Utility. And it deletes some system caches, including font caches and the kernel cache, which are automatically created again as needed." if it doesn't happen when in safe mode, restart your Mac and test again. 

3. Create a test user to see if it is something only related to your user account: Set up users, guests, and groups on Mac.

• If it happens in multiple accounts, run First Aid on your Mac by following How to repair a Mac disk with Disk Utility.

Hope this information helps. 

Have a good day.

If you have 100's of % kernel_task CPU usage, then your Mac is overheating. The kernel_task will put the intel chip into a low power idle mode to let it cool down and keep from melting (literally). This makes the scheduler think the kernel_task is using a lot of CPU.

The overheating could be because you are trying to do too much with the Mac (lots of processes running doing lots of graphics, CPU, I/O, etc...).

It could be because your Mac is in a very hot environment, and/or the cooling vents are blocked.

Most likely is you have an accumulation of dust/pollen/smoke particles inside the Mac's cooling fans and cooling fins which is preventing the Mac from getting rid of the excess heat.

Please run Etrecheck and post its full report here.

Use the “additional text” button and paste the report into the text box.