2020 Intel iMac crashes during MacOS update. Only fix is to reinstall OEM 8GB RAM

There's a long history with my 2020 iMac. I ordered it brand new through Adorama with 8GB. On my request, Adorama installed 128GB RAM (from OWC) and shipped it to me that way. They also sent me the original 8GB RAM that was in the iMac.

The iMac immediately started having stability problems whenever it was put under load. Running idle was fine, but the moment I started multitasking, or running Lightroom, the machine would freeze and shut down. I could duplicate it like clockwork. I sent it twice to an Apple service center to investigate the cause, they said they could not duplicate it. Took it home, within 10 minutes of use it would freeze. Memtest86 would say the there were problems with the RAM.

I then decided to install 128GB RAM from Crucial. This was three months after my original purchase. Immediately after installing the Crucial RAM and turning it on for the first time, I immediately noticed the iMac running different. No fans, very quiet, and was 100% stable. Ran fine for years this way.

Then MacOS Sonoma arrived.

When installing MacOS Sonoma, a prompt displayed on my iMac that a firmware update was required in order to install MacOS. Immediately after the update, my Mac would freeze and shutdown during the install process. The fans would first turn on at full speed for a second, then the machine would shut down. It was behaving exactly as it did when it was running on OWC RAM. I would reinstall my 8GB OEM RAM and everything works fine.

So whatever that firmware update did, it made my system unstable again after years of flawless operation.

So I'm back at the beginning again. Crucial is sending me a replacement 128GB RAM modules so I'm really hoping it works. I spent $7K on this iMac and it was the worst Mac I've ever owned.

I agree that there is a problem with the RAM. I'm also pointing the finger at Apple as I believe Apple is not being up-front with what it's doing on the firmware side or system side and not relaying that information to the RAM companies.

I'm just hoping that when I receive the new RAM, by it being "newer", maybe any changes/updates/firmware/etc.. might have been applied to these RAM modules and will play nice. Otherwise, I will most likely end up retiring this machine way earlier than I want and purchase the next Mac Studio later/next year.

My iMac is a 10-core i9, 8TB SSD, and 128GB RAM. It's still a very fast machine and I was hoping to use it for at least 5-7 years and buy whatever new M-base Mac at that point. Such a waste.

Please. Spare me the philosophical checklist.

I've owned several iMacs over the last 15 years. I've always upgraded the RAM with zero issues. My 2020 iMac is the only one that ever experienced this issue. The Crucial RAM I use are the same OEM chips used in Apple iMacs and was working perfectly for years up until Apple did some kind of firmware update that started causing my issues.

I spoke with a support rep at Crucial and for what it's worth, they are sending me replacement RAM modules.

This is the only iMac I ever owned that gave me problems. My next Mac will be an M(x)-based system so this problem will be forever in the past.

I'm guessing that you too are using 3rd-party RAM?

I contacted Crucial, and as the RAM has a lifetime warranty, they are sending me replacement RAM modules. What's baffling to me is that the Crucial uses the exact same chips used as Apple OEM. As my iMac works perfectly when I reinstall the OEM RAM memory, I suspect there is a firmware issue that Apple is not fessing up to.

I get you. I also have an M2 MacBook Pro. Sonoma works perfectly on that. I've had nothing but horrible experiences with Sonoma on my Intel-iMac. Monterey worked perfectly but I want to remain current on MacOS (shocking I know) in order to keep up with all security updates.

Apple stopped selling the 27" iMac in 2022. That's barely two years ago. It's like Apple just stopped caring for all those customers that are still out there using their fairly-recent Intel-based Macs. Sonoma is just horrible for Intel Macs, but particularly painful for the 27" iMac owners with 3rd-party RAM.

This thread is from 2021. Back then, yes... my Crucial RAM worked perfectly the moment I turned on my iMac for the first time with the replaced RAM.

Whatever Apple did with MacOS/Firmware on the 2020 iMac, it basically broke the stability of the system. I am hoping to get the replacement RAM in the next few days. For now, while my iMac is working with the OEM RAM, it's only 8GB and working in Lightroom and Photoshop with 8GB is painfully slow.

And yes, I do know to order a new Mac with expected RAM I will need. Considering the time and headaches of using 3rd party RAM, I should have just bit-the-bullet and ordered Apple's crazy-expensive 128GB RAM option to begin with.

It would not surprise me if Apple went the soldered route with iMac RAM to remove the headaches of dealing with 3rd-party RAM and the stability issues.