iMac Fan issues

[HMAletter]

Late 2012 27" iMac, 16 GB 1 TB Fusion drive, i7 chip.

Since April on and off with this issue. Fans goes whirring, everything slows down until you have to shut it off. It can go several days (or not), with everything fine. No ryhme or reason.

I've done the basic things at least 3-4 times, up until this week when I installed a new version of 10.13. Nothing's changed.

I do notice each time the fans start running at high speed, a fair amount of little dusties come out.

But, I did setup another admin user, and Zero problems with that. I haven't just switched over because I kept getting app and permission problems. Particularly, my Parallels and Windows comes up blank with the new admin user. I've also run the deep disk utility.

I have this great fear of a fresh install, which means going into time machine and retrieving all of my apps and stuff.

Anything else I can try?

 

[wardie]

Are you sure you’ve not got a rogue process chomping up all your CPU and effectively grinding the system to a stop? Use watch activity monitor - load it up on login so it is there ready...

 

[HMAletter]

I have it running all the time now yes. Early on one of the CPU choppers was the photo process running. That's when I realized I was better off not upgrading to this version. But that went away after it was finally done. Nothing else out of the ordinary.

 

[HMAletter]

and now, the Fusion Drive is not accessible. No first aid, no boot, not able to restore from clone or time machine.

Now I look at the options, and wonder how Apple created an iMac so hard to replace the hard drive.

 

[mikehalloran]

These are very easy to service. They're held together with double-stick foam tape. A guitar pick works great but the plastic pizza wheel is faster.

To replace the HDD—99.44/100% likely to be your problem—you will need a drive, preferably an SSD, a temp sensor. OWC sells tool/sensor/tape kits for these.
https://www.amazon.com/OWC-Digital-Thermal-Sensor-Upgrade/dp/B00J42HP9O/ref=sr_1_5?ie=UTF8&qid=1543386526&sr=8-5&keywords=owc+temperature+sensor&th=1

Recommended bracket
https://www.amazon.com/Fenlink-Inte...-7-acs&keywords=2.5+to+3.5+hard+drive+adapter

Do not buy one of their overpriced, underperforming SSDs—instead, a Samsung 860 EVO is better and less expensive.
https://www.amazon.com/Samsung-Inch-Internal-MZ-76E1T0B-AM/dp/B07864WMK8/ref=sr_1_1?ie=UTF8&qid=1543386438&sr=8-1&keywords=860+evo&th=1