kernel_task issue with imac 27" late 2015

1. Your computer is really a mess. First, you have CleanMyMac installed which at best is 100% unnecessary and at worst can modify Mac OS which I believe it has. The reason I believe this is your Apple security has been disabled. Actually I was being kind be using the word "unnecessary", it's really akin to malware and should be uninstalled ASAP (today) by following the developers instructions. Then run another EtreCheck report and study it to see if you can find ANY evidence of CMM. If you can then you need to download FindAnyFile and have it look for anything that says CleanMyMac and get rid of it!
2. Next, to rectify the Apple security problem you need to restart in the Recovery Partition (hold down Command + R on startup) and install Mac OS, this type of install will not affect your data however ALWAYS have a backup of your system. This. type of install will install any missing or damaged portions of Mac OS.
3. Finally, your 256GB SSD is running out of space which is also a problem. You need to offload some of your data to an external drive. For most users photo, music & movie libraries take up the most storage. Once you have an external drive offload those libraries to the external drive. If you do not know how, please read Move your Photos library to save space on your Mac to get a good idea.

It will help us get a good idea of what is causing your problem if you provide a report of your system, that way we do not have to play 20 questions with you. The report we are requesting does NOT provide any personal information and is extremely safe to use. Please navigate to www.Etrecheck.com and download the free version of EtreCheck. Once you have you downloaded the app and installed it, please run the report and save it. This report will help us get a good idea what has been installed on your system and help us be able to diagnose what may be wrong.

When you have your report, you can attach it when you reply to this message and we can then review it and help you determine what is needed to get your system running well again. 

For instructions on how to download your EtreCheck report and attach it to your reply to this message please click How to use the Add Text Feature When Post… - Apple Community

And you can game no problem on any modern Mac. Absolutely no concern at all! Apple SSDs are built-to-last with high endurance, performance, and reliability. Don't worry about installing any apps externally or anything special. Just use the Mac as you'd like.

Also, for a new 27-inch desktop Mac setup, I'd recommend a Mac mini and a Studio Display. A modern Apple silicon Mac mini is far more powerful and capable than your iMac.

Mac mini - Apple

Studio Display - Apple

Jack

Besides uninstalling CleanMyMac according to the developer's instructions unless you're using a true VPN tunnel, such as between you and your employer, school or bank's servers, they are useless from a privacy standpoint.  Read these two articles: Public VPN's are anything but private and Former Malware Distributor Kape Technologies Now Owns ExpressVPN, CyberGhost, Private Internet Access, Zenmate, and a Collection of VPN “Review” Websites. 

You can check to see if you've removed all of the supporting files by downloading and running the shareware app Find Any File to search for any files with the application's or the developer's name in the file name.  For CleanMyMac software you'd do the following search(es): 

1 - Name contains cleanmymac

2 - Name contains macpaw

Any files that are found can be dragged from the search results window to the Desktop or Trash bin in the Dock for deletion.

FAF can search areas that Spotlight can't like invisible folders, system folders and packages.  

mikeypas wrote:

Cleanmymac serves its purposes. I understand the debate about it, but I install it from time to time to uninstall apps or to check my startup items etc.

whatever your opinion of it, it’s not causing kernel_task to go to 300% because it was doing that even without cleanmymac installed.

same with the SSD, it’s not causing the cpu to go to 80c.

CleanMyMac is bad news, I'd remove it (uninstall completely). The problem is it infiltrates the OS and interferes with normal operations. In some instances, users have found that CleanMyMac "cleaned" out essential files without which the computer stops working normally. CMM is one of the most common reported causes of problems in Apple Discussions.

That said, it is your choice to stay with it.

I am concerned about the SSD. With only ~ 10% free space, it will be working very hard to page to disk and manage virtual memory. One symptom of this could be overheating. Also, Etrecheck reports your disk is performing poorly, possibly failing:

Write speed: 253 MB/s

Read speed: 1683 MB/s

The read speed is ok, but the write speed is very poor, maybe 10-20% of what it should be. I have external bus powered SSDs that are 5 times faster than that. I am suspecting that the internal SSD could be degraded or failing. One way to check this is to download DriveDX and look at the SMART parameters. Run the extended (long) test -- not just the short test. The extended/long test may take 20 minutes or so but may reveal something. The other parts of the report will provide information on how much life is left in the SSD.

Cleanmymac serves its purposes.

No it doesn't!

However, I understand your hesitation to uninstall CleanMyMac. Marketing tactics from these companies and tech-focused publications, often sponsored by the anti-virus & cleaning companies, "scare" users into installing anti-virus and cleaning software.

And I have some family members who felt the same way for quite some time. They switched to the Mac from Windows PCs, and for some time didn't understand that the Mac is, in fact, different, and didn't need any of these anti-virus and cleaning apps. Unfortunately, a while back, a family member of mine had to learn that CleanMyMac had to go the hard way a while back. During one of CleanMyMac's automatic "cleans", it damaged her Photo Library, apps, and other miscellaneous files. Thankfully, she had a Time Machine backup to restore from, but it goes to show that CleanMyMac, and similar products, cause a lot of damage. In addition, until the day she deleted CleanMyMac from her Mac, she occasionally had all kinds of oddities, from slow system performance to odd pop-ups from CleanMyMac that were advertisements (just like adware).

Please consider to delete it.

Jack

My guess is your SSD’s failing. Their fail rates are much higher especially when subject to the kind of use you’ve described. Looks like a lost cause to me; I’d replace the entire system with new, and if/when you do that: treat your SSDs with more TLC - install heavy disk-use Apps on an external. If gaming is what you use the system for, consider moving to Windows and/or Apple TV. Good luck!

That’s ok, none of the machines including the Mac Studio are meant for disk-demanding gaming. SSDS can fail on them too if constantly overworked. Get one custom-built for Windows instead. At least you can swap the disks easily. All the best!

Once the SSD gets worn, it can slow across-the-board which in turn can result in the CPU working harder. Your iMac is slowly but surely grinding to a halt. Backup data while it’s still alive and have Plan B ready. Good luck!