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Alarmingly High CPU Temperature on 2020 27" iMac
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Isn't 127C just the default 'reading' when there is no reading or sensor? Pretty sure your CPU would have cooked at 127C.
I'm getting readings from the CPU die, so it doesn't look like it a default measurement. Idle is 85º C and when I start Cinebench, I see it rapidly increase to 127º C.
Those numbers are 100% incorrect. Intel CPUs have a thermal shutdown point to protect themselves. I'm not quite certain what that trip temperature is but it is somewhere in the vicinity of 100°C. Fanny is simply not compatible with the 2020 iMac and its 10th gen CPUs yet.
Macs Fan Control reports CPU cores 1, 2, and 4 at only 100º C, which seems way more normal. Well, normal for an iMac. That's still uncomfortably high, but at least not meltdown-level high.
But this is still terrible news. 100°C is too much, even though considered "ok" for Macs. But what's really bad is the reported fan speed in your screenshot. That's full speed! Way too noisy. I wonder what the CPU frequencies are. Please try Intel Power Gadget. Can someone with the i7 10700K also report on fan speed and CPU temperatures?
Only 99.7º C in Intel Power Gadget. I'd also like to see some readings from others with the 2020 27" iMac.
I take the first graph to be CPU power. Seems to be running at 80W constantly, above the nominal 65W TDP rating.
So actually that's "ok": runs at 4,2Ghz well above base frequency (3,3Ghz). 2700rpm would be too much noisy for me, but at least you get some good CPU speed in return and it seems to be holding that frequency despite high temperatures.
Thanks for testing. Now we need some results of the i7 and i9 in comparison (educated guess: The i7 will run cooler because of the soldered heatspreader used).
If you want to experience what 2700 rpm feels like, check out this video:
So actually that's "ok": runs at 4,2Ghz well above base frequency (3,3Ghz). 2700rpm would be too much noisy for me, but at least you get some good CPU speed in return and it seems to be holding that frequency despite high temperatures.
Thanks for testing. Now we need some results of the i7 and i9 in comparison (educated guess: The i7 will run cooler because of the soldered heatspreader used).
If you want to experience what 2700 rpm feels like, check out this video:
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Cinebench, Intel Power Gadget, and Activity Monitor with CPU Usage, CPU History, and GPU History graphs enabled.
100 °C is not "too much" but within Intel's thermal specifications. Just because we as humans rarely feel comfortable at temperatures of 100 °C doesn't mean the same holds true for computer chips. Unlike other manufacturers Apple is known to prefer quiet operation over low temperatures, and the engineers take Intel's specs and run the CPUs right at their respective thermal limit. And we have yet to witness a single failed Intel CPU due to excessive heat.
GPUs? Like flies.
Shoddy caps? Yes, occasionally.
CPUs? Not one.
GPUs? Like flies.
Shoddy caps? Yes, occasionally.
CPUs? Not one.
Look, I don't see any "quiet operation" here. This thing is noisy as hell at full blast 2700 rpm. There is no more headroom. And this machine is brand new, so after a year or so with a bit of dust accumulated you can bet performance will degrade.
Of course it is. Under full load. That energy has to be dissipated somewhere. I know, I know, stupid physics, but even Steve's reality distortion field was unable to overcome the laws of physics 
What I meant is that Apple is known to keep the fans on low speed for as long as possible rather than ramping them up at 60 °C already, like many other manufacturers do. At full load they are just as load because, again, physics.
What I meant is that Apple is known to keep the fans on low speed for as long as possible rather than ramping them up at 60 °C already, like many other manufacturers do. At full load they are just as load because, again, physics.
I don't agree. They are at full blast because of a poorly designed cooling system and Intel using thermal paste instead of solder. Just look at the iMac Pro. Fans don't ramp up under load even though that CPU dissipates more heat!
I don't agree. The iMac's cooling system is not poorly designed. It is, however, also not designed for constant 24/7 maximum load because that's not what normal users tend to do. The iMac's cooling system was designed with its primary target audience in mind, which is not necessarily professionals. Professionals tend to run much more demanding tasks, which is why the iMac Pro's cooling system is completely different from the iMac's.
In return, the iMac's fans stay virtually silent until the temperature is close its trip temperature whereas other manufacturers keep it at or below 70-80 °C. Case in point: go browsing the web with a 16" MacBook Pro and with an equally expensive and similarly powerful Dell XPS 15 or Lenovo ThinkPad T15. Both will ramp up their fans much sooner than the MBP.
But hey, you're free to disagree with me as much as you want and have your own opinion. No harm done. Maybe the iMac is not the right computer for you. Maybe you're better off with an iMac Pro or a Mac Pro, both of which tend to run much quieter under load.
In return, the iMac's fans stay virtually silent until the temperature is close its trip temperature whereas other manufacturers keep it at or below 70-80 °C. Case in point: go browsing the web with a 16" MacBook Pro and with an equally expensive and similarly powerful Dell XPS 15 or Lenovo ThinkPad T15. Both will ramp up their fans much sooner than the MBP.
But hey, you're free to disagree with me as much as you want and have your own opinion. No harm done. Maybe the iMac is not the right computer for you. Maybe you're better off with an iMac Pro or a Mac Pro, both of which tend to run much quieter under load.
Yes, and I beg to disagree again. Because I'm not talking 24/7 loads here. Just look at the video I posted above about the 2017 iMac which probably reflects the 2020 iMac's behavior. After 10-20s or so the fan ramps up to full speed (edit: only applies to the i7 7700K 2017 iMac).
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I believe iMac's cooling system is poorly-designed for these current Intel processors, but I also believe iMac is not the right system for professionals.
This iMac was designed in 2012. Intel's CPUs weren't as awful back then as they are now. Since 2015, they've been stuffing more and more cores at higher frequencies into largely the same chip. iMac's single-fan configuration just can't handle that well. The cost for Apple to add a second fan with all the available space in iMac would have been minimal, but they've clearly shifted focus to Apple Silicon, which I believe is the correct choice.
This iMac was designed in 2012. Intel's CPUs weren't as awful back then as they are now. Since 2015, they've been stuffing more and more cores at higher frequencies into largely the same chip. iMac's single-fan configuration just can't handle that well. The cost for Apple to add a second fan with all the available space in iMac would have been minimal, but they've clearly shifted focus to Apple Silicon, which I believe is the correct choice.
That video does NOT reflect the 2017 iMac's behavior at all. Not even close. Let me explain.
Disregarding the fact that he is running Cinebench Multicore, a maximum CPU load scenario that rarely ever (aka: practically never) occurs in the real world he's running that benchmark on the 95W 4.2 GHz Core i7 CPU that the iMac was never designed for. The iMac's cooling system was designed for 65 W CPUs, not 95 W CPUs. Part of why Apple is now switching to Apple Silicon is the fact that Intel was unable to produce low to medium power high-performance CPUs but instead simply started increasing thermal limits. Apple had no choice but to opt for high-performance high-power chips to satisfy the performance-hungry crowd of semi-professionals and professionals looking for the best bang for the back. Just for funs and giggles I ran the Cinebench R20 multi-core benchmark on my 2017 Core i5-7500 quad-core iMac running at 3.4 GHz with a Turbo Boost of 3.8 GHz. I had the fan set to Auto idling at 1,200 rpm, and that's exactly where it remained throughout the entire test. CPU temperatures peaked at slightly over 70 °C and even after more than four minutes of non-stop maximum load my fan was still pegged at 1,200 rpm. Now, with a 95 W CPU this is a very different story but that fact has been well-known since 2015.
I'm still busy working right now but I will create and upload a video to YouTube later tonight proving how long it will take for my 2017 iMac to start ramping up its fans at all, and what it actually takes to have them running full blast.