iMac 27-inch 2017 RAM problems

I did not see any mention of the brand of RAM you tried however you should know iMacs are very sensitive to quality RAM. Most experienced users on these forums only use Crucial.com (buy it direct) or OWC (www.macsales.com) because both vendor sell quality RAM at reasonable prices and provide excellent service.

I have the exact same problem. My computer runs with the apple supplied 2-4GB ram or the 2-16GB Crucial ram, but when installed together, the computer will not boot. I called apple. Was put on phone with a higher up when lower level support could not help. Never got a solution. But, I guarantee Apple knows about the issue. Currently, I'm using my computer with the Crucial ram, but not happy that I can't have the original 8 GB in at the same time.

Crucial RAM should be purchased directly from Crucial and not a reseller, yes even Amazon. iMacs are sensitive to high quality RAM and on occasion resellers will sell RAM that is not the highest quality. If you have the original RAM remove the Crucial RAM and test the computer. If it stabilizes then you know it the RAM from Amazon. If you need to return it, purchase Crucial direct from Crucial or buy OWC (www.macsales.com) RAM.

Good luck.

I agree with this advice - best to buy direct from Crucial. But, like a lot of folks, the desire to save money drove me to buy my 64gb of ram from cheaper source. When installed I was having various problems and two sticks routinely failed the TechTool Pro 9 ram test - the best ram testing app I had access to. Apple hardware test was useless. Two of my 4 sticks were manufactured by Crucial and two by Chip Express. The problem was with the Chip Express ones. I contacted my source and he offered to replace them with two sticks that he stressed tested using MemTest for 48 hours. Once they passed this test he shipped the new sticks to me (they were still labeled as manufactured by Chip Express), and they passed my TT Pro 9 test and my own version of Memtest which I acquired in the interim. Now, I have zero problems and though I had a bit of hassle, I did save more than a thousand over Apple ram and several hundred over buying direct from Crucial. Perhaps the one insight I may have is if you are having problems it most likely the ram itself rather than the ram not playing nicely with the installed Apple ram as I never saw any such problems and I ran both sets with and without the 8gb of apple ram installed.

I can't speak for the 2017 iMac, but I can speak for buying from amazon. I upgraded my late 2015 iMac with 1 16 2x8 curcial kit and had no issues with the new ram and stock apple RAM. I ended up getting a second kit, just to have an equal 32 GB. That was back at the beginning of the year when I purchased the iMac (before ) the refresh was ever a thing), and I have had zero issues.

Like I said, can't speak for the updated hardware. Just wanted to share a success story I had with ram upgrades, and saving money too.

Did you buy the Crucial RAM directly from Crucial or from a Crucial reseller?

Crucial ram purchased on Amazon.

Glad it's working okay again.