iMac fan runs constantly; how to downgrade macOS?

You would need to erase the hard drive and install another version from scratch using a bootable USB drive or macOS Recovery.

Make sure you backup any files and data you want to preserve as returning to a previous macOS version is a fully destructive process and will erase everything.

click here ➜ Use macOS Recovery on an Intel-based Mac - Apple Support

or here ➜ Create a bootable installer for macOS - Apple Support

With that said, fans running means the CPU and other components need to be cooled down. Having the fans run means the components won't overheat. After an update it's normal for the CPU to work harder than normal to finish up background tasks. It should after a few days return to normal though.

There’s a legacy kernel extension installed at /Library/Extensions/Soundflower.kext

It is currently loaded

It’s Soundflower (com.Cycling74.driver.Soundflower)

Built by Matt Ingalls, version 2.0b2

Compiled against SDK 10.10 (Yosemite) — which is ancient by macOS 26 Tahoe standards

If you still need virtual audio routing:

BlackHole (most common modern replacement)

Loopback (paid, very polished)

Audio Hijack (for capture + routing)

All of these use modern, supported mechanisms and won’t rely on crusty kexts from 2014.

Fans run on a thermostatic system that detects increased heat on/in various components. Immediately after major upgrades, fans may run more as the computer continues to do housekeeping required by the update. However this should be complete in a few hours at most

I encountered no fans issues in either our M4 iMac 24" or our M4 Pro Macbook Pro after upgrading from Sequoia to Tahoe.

Increased fan activity tends to be associated far more with work station arrangement that affects cooling, and useless aftermarket utilties. Exactly what Mac model and sub-model do you have? That may affect how we approach your issue in this setting.

The single best way for us to help where a "hands-off" diagnosis is all we have is for you to post a system config report. Fortunately there is a safe secure way to do that, designed expressly for use with these forums.

If you want a data-driven evaluation in this setting where we can neither see nor touch your computer, please post an EtreCheck report. We can quickly and within the limitations of these forums help you determine what issues are at play without our playing a protracted game of "20 Questions" with you that could go on for days. 

EtreCheck Pro is available here: https://etrecheck.com/index

The free version will do nicely for this purpose, although the app is worthy of our financial support.

We can see hard data about drive performance, software issues and interferences, and RAM usage. Etrecheck is the development of a long-serving and trusted ASC contributor. It is a reporting app, not a "fix-it” app, expressly for displaying information in these forums to help us help you remotely. It will not reveal any personal or secure information.

Please see this excellent user tip on how to post long text reports like EtreCheck's into a forum response:

How to use the Add Text Feature When Post… - Apple Community

Please post the entire report. What seems insignificant to a new Etrecheck user can speak volumes to those of us who have reviewed thousands of those reports. 

Thanks Becky. It posted without issue.

I see a pretty healthy-looking iMac. Your storage SSD is running at expected speeds and shows healthy, and I only see Adobe apps that are always going to up the workload and potential turn on the fans. Pro apps, ya know.

Fans' controlling hardware are under the aegis of the System Management Controller (SMC). In addition to what our HWTech has wisely recommended, you may find an SMC reset helpful. See:

Reset the SMC of your Mac - Apple Support

Your iMac has the "T2 security chip" so use the instructions in the article section, "Mac with the Apple T2 Security Chip— Desktop computer"

For the sake of testing, try running with the Seagate external drive disconnected. Not on my "usual suspects" list but I have reviewed reports where an entry-level US external drive slowed performance. An easy check.

Sometime a seconds restart after and upgrade is beneficial.

Allan

Bcky555 wrote:

What I can relay right now is my iMac's fan hardly ever ran before the update to 26.

As stated it is normal for the fans to ran immediately after the update to reindex the files and usually lasts for a a day or two. Beyond that you probably have a third party app that is not compatible and may need to be updated. That is the purpose of the EtreCheck report.

One example is some apps were built with the Electron framework that was found to be using a Private API not supposed to be used by Developers and that framework has since been updated, but apps that used the framework would need to provide their own update built with the that framework. Affected apps caused increased CPU/GPU use with the fans running excessively.

https://macos-tahoe.com/blog/macos-tahoe-electron-apps-performance-complete-guide-2025/

I concur 100% with Allan Jones.

Download and run EtreCheckPro, then post your EtreCheckPro report before resorting to more drastic measures.

Bcky555 wrote:

Good Morning Allen, I think I did this correctly! I did read through all the posts here and the info is way over my head! so hopefully this info will tell you what is wrong and can help me to get my Mac to normal.

I updated to 26 about 3 days ago.

<report.log>

I'm not a macOS software expert, but to get you started try these things. If you do them one at a time & wait, you may be able to discover which item was involved with the problem (sometimes it is a combination of items which may have compatibilities with each other, but work "fine" by themselves):

• Turn off MalwareBytes' real-time scanning option. No reason to have it running 24/7....really no reason to have it installed unless you suspect you have been infected with malware or adware. There should be an option on one of MalwareBytes' menus for turning off real time scanning protection....also one for uninstalling the app.
• Turn off Apple's Artificial Intelligence found in the System Settings
• Make sure all of your third party software is completely up to date especially the Paragon NTFS driver & the Wacom software since they need constant updating when new macOS updates patches are installed.

Bcky555 wrote:

I removed the Wacom as I no longer use it.

You should run EtreCheck again to make sure all references to Wacom are gone. Sometimes the app developer's uninstaller doesn't always clean up everything.

That paragon thing showed up when I bought the new EHD a while back. I will need to figure out how to update it.

If you are not using the NTFS file system on any of your drives, then you can follow Paragon's instructions to uninstall that software. No sense having it running all the time if it will never be used since it could possibly cause problems at some point if it is not being updated/maintained.

And a great suggestion by @Allan Jones for trying an SMC Reset.

Also worth reading in this situation About fans and fan noise in your Apple product - Apple Support

Which exact model iMac do you have?

Before proceeding make a Time Machine Backup 

Unload it (if still loaded) which it appears to be loaded 

Finder >> Go >> Utilities >> Terminal 

In the Terminal application use this command 

sudo kextunload /Library/Extensions/Soundflower.kext

Do not worry if an error message is presented just continue to next step 

Still in the Terminal application 

Use this command 

sudo rm -rf /Library/Extensions/Soundflower.kext

Sill in Terminal application use this command 

sudo kmutil install --update-all

A Reboot is Mandatory.

To avoid possible Typo errors

Copy and paste into Terminal each of the 3 commands in the order that are presented

Command 1 >. sudo kextunload /Library/Extensions/Soundflower.kext

Command 2 >> sudo rm -rf /Library/Extensions/Soundflower.kext

Commad 3 >>> sudo kmutil install --update-all

If you can't control the fan, might as well use Mac Fan Control to over ride macOS and see, the fan control also provides a estimate of compont temp, Use at ur own risk, not made by apple.

If you have an Intel Mac the fans are controlled by the SMC. To reset the SMC follow the instructions in this Apple document; Reset the SMC of your Mac - Apple Support

Recently upgrading from Sequoia to Tahoe recently I was not surprised to see my fan running faster for a couple of days, as this has occurred for every update for a long time. It settles down eventually. Before doing anything drastic I would give it a while.

On another note, being very disappointed with Tahoe , I attempted to downgrade to Sequoia and found that a new install of Sequoia I could install but could find no way to import all my files/data from time machine that had backups from both Sequoia and Tahoe. After a day of research and not finding a way, I reinstalled Tahoe and am stuck with that. In the past I have reverted to an older OS but does not seem very possible anymore. I run a 2020 iMac and from what I have read trying to revert to a M1 or new iMac is fraught with even more problems and not recommended by many on this Board.