Quite. The other thing I’ve found to counter this on my machine is disabling turbo boost has a dramatic effect on fans and on the temp a bit. Takes core temps down 100C->90C but the fan then goes from max like 2700rpm right back to 1200rpm constant running. But that’s on the 2017 i7 7700K where base freq is 4.2GHz anyway and turbo only ever seems to kick it to 4.4GHz, so not a lot of speed lost, as it maintains 4.2GHz OK like that.
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Alarmingly High CPU Temperature on 2020 27" iMac
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Quite. The other thing I’ve found to counter this on my machine is disabling turbo boost has a dramatic effect on fans and on the temp a bit. Takes core temps down 100C->90C but the fan then goes from max like 2700rpm right back to 1200rpm constant running. But that’s on the 2017 i7 7700K where base freq is 4.2GHz anyway and turbo only ever seems to kick it to 4.4GHz, so not a lot of speed lost, as it maintains 4.2GHz OK like that.
I was surprised (and pleased) that the cooling system in the 2020 iMac i7 was able to keep the temps just below 100c and the i7 in turbo boost for the whole Cinebench 2.0 benchmark.
A better look at the Power, Freq and Temps during and just after the Cinebench 2.0 benchmark.
GetRealBro
HandBrake trans-coding .ts into .mp4 on the same 2020 iMac, 3.8GHz 8 Core i7, Radeon Pro 5500 8GB, 8 GB RAM, 2TB SSD.
HandBrake didn’t push the system as hard as I expected. It fairly quickly settled into a steady state with the CPU in mild Turbo boost, temps just below 100C AND 15-20% CPU idle!
HandBrake 4.36.26.jpg — Soon after kick off.
V
HandBrake 4.41.45.jpg ^ — A little while later, the Power, Freq and Temps are holding steady.
GetRealBro
HandBrake didn’t push the system as hard as I expected. It fairly quickly settled into a steady state with the CPU in mild Turbo boost, temps just below 100C AND 15-20% CPU idle!
HandBrake 4.36.26.jpg — Soon after kick off.
V
HandBrake 4.41.45.jpg ^ — A little while later, the Power, Freq and Temps are holding steady.
GetRealBro
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The Macs Fan Control window is included in the CineBench benchmark images in this post…
Alarmingly High CPU Temperature on 2020 27" iMac
For comparison to my 2018 Mini i7… Cinebench running on a 2020 iMac, 3.8GHz 8 Core i7, Radeon Pro 5500 8GB, 8 GB RAM, 2TB SSD. iMacBench1 — Core temps a little over 40C with a fan at 1,200RPM under minimal load. iMacBench2 — Under full load All 8 cores increase quickly to turbo boost then...
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In the HandBrake test, the fan had just reached full speed (2,700rpm) when I took the first screen shot at 4.36.26 and remained at full speed till the job was finished plus a little cool down period.
BTW I was pleased that the 2020iMac fan at 2,700rpm is basically white noise. It is audible but not really annoying in a room with even a little background noise. UNLESS… the iMac is set close to a hard surface e.g. a wall, which reflects the sound back toward the user.
GetRealBro
Were you ever able to get memtest to work? I tried and it said something about can’t boot from external dock
Did you enable booting from External as shown here? https://support.apple.com/en-gb/HT208198
I now own a 2020 8 core i7 iMac that arrived in September.
Before seeing this thread I've been alarmed by the fan noise and then installed a temperature gauge app.
I frequently use Handbrake to convert video file formats. The old 2013 i5 machine chugged through this silently, and the widget-based temp sensor that was all I used at the time never got overly hot.
The new machine whizzes through the tasks about 5-10 times faster but the fan rockets to 2700rpm and the temps of all cores redline and hover there for the duration which is concerning.
I was concerned enough to call Apple as I thought maybe something was damaged during shipping.
I was told this was normal.
A few months in and this behaviour has continued.
The machine has shut down from overheating at least 4 times that I've witnessed.
My temporary fix is to run a $10 USB powered fan behind the machine pointed at the hotspot. This tends to keep the temps when under load to around 94-99 degrees.
Looking through the forum, it would seem that I'm not alone, so accidental shipping damage is unlikely.
I am concerned for this machine's longevity though, with this kind of thermal stress being applied. Not to mention the annoying fan noises
Has anybody come up with a fix for this?
Before seeing this thread I've been alarmed by the fan noise and then installed a temperature gauge app.
I frequently use Handbrake to convert video file formats. The old 2013 i5 machine chugged through this silently, and the widget-based temp sensor that was all I used at the time never got overly hot.
The new machine whizzes through the tasks about 5-10 times faster but the fan rockets to 2700rpm and the temps of all cores redline and hover there for the duration which is concerning.
I was concerned enough to call Apple as I thought maybe something was damaged during shipping.
I was told this was normal.
A few months in and this behaviour has continued.
The machine has shut down from overheating at least 4 times that I've witnessed.
My temporary fix is to run a $10 USB powered fan behind the machine pointed at the hotspot. This tends to keep the temps when under load to around 94-99 degrees.
Looking through the forum, it would seem that I'm not alone, so accidental shipping damage is unlikely.
I am concerned for this machine's longevity though, with this kind of thermal stress being applied. Not to mention the annoying fan noises
Has anybody come up with a fix for this?
Absolutely nothing about that behavior sounds remotely normal. It’s doubtful there would be any sort of “fix” short of getting the machine serviced.
The CPU cores are designed to run up to 100 degrees C, and the fan is designed to run at 2700 rpm, continuously, this is normal. However shutting down from overheating is not normal. How do you know it is shutting down from overheating? The CPU should throttle its frequency to avoid overheating above 100 C.
I suggest stress test it by running Cinebench R23 multicore test continuously for 30 minutes. This will take the CPU core temperature to 100 C and the fan to 2700 rpm. If this does not shut it down, then overheating is not likely the cause of shutting down.
While you run Cinebench R23 multicore, also run Intel Power Gadget to monitor the CPU temperature, power consumption, and clock frequency to see if the CPU is throttling.
Here is a screen shot of what it looks like on my 2020 8 core i7 iMac (same as yours) - I have had no shutdowns:
You can see the CPU has throttled to 4.4 GHz to keep the temperature below 100 C.
Pointing a fan at the iMac is unlikely to reduce the CPU temperature when all cores are running at full utilization. The CPU will just increase its clock frequency until the core temperature is just below 100 C. The CPU will strive to run at the fastest frequency it can that does not cause the temperature to rise above 100 C.
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I finally had a chance to download and run the two apps mentioned above.
During the CinebenchR23 test, the CPU temps never got as high as it did during Handbrake. Maxed out at 96degrees with fan speed going to 2700rpm and without the external fan I'd been using turned on.
With the Intel Gadget app, I was seeing the same results, just less detail, although I was able to observe the clock speed variation that was mentioned, and it did drop slightly during the Cinebench test.
I should be able to render some more videos in the next couple of days and report back the results.
The only reason that I thought that my iMac was shutting down due to overheating was that it was working hard, running very hot with all 8 cores going to 100 and staying there for several seconds each for a good while- 15-30 minutes - and then the machine would shutdown. The temperature gauge app would report an abnormal shutdown when I next launched it after a shutdown like this.
Since it has happened on multiple occasions with different files being read from different drives in an app that works fine on our other 2 older iMacs (just lots slower) then assumed heat was the cause.
I'll try calling Apple support when I have more time, possibly next week.
During the CinebenchR23 test, the CPU temps never got as high as it did during Handbrake. Maxed out at 96degrees with fan speed going to 2700rpm and without the external fan I'd been using turned on.
With the Intel Gadget app, I was seeing the same results, just less detail, although I was able to observe the clock speed variation that was mentioned, and it did drop slightly during the Cinebench test.
I should be able to render some more videos in the next couple of days and report back the results.
The only reason that I thought that my iMac was shutting down due to overheating was that it was working hard, running very hot with all 8 cores going to 100 and staying there for several seconds each for a good while- 15-30 minutes - and then the machine would shutdown. The temperature gauge app would report an abnormal shutdown when I next launched it after a shutdown like this.
Since it has happened on multiple occasions with different files being read from different drives in an app that works fine on our other 2 older iMacs (just lots slower) then assumed heat was the cause.
I'll try calling Apple support when I have more time, possibly next week.
Geez that's ridiculous lol.
I have a 9700k in my desktop tower and getting over 70c is an accomplishment. That's like after an hour of gaming, and at that point the fans will be rather audible as I have them set to spin up pretty far if the CPU is approaching 80c.
One thing I wonder is how bad the thermals get when you have a 5700xt in the iMac. Mine has a beefy heatsink and gets very hot/noisy after gaming for a while (90-100c). I can imagine that thing frying a hole in the back of an imac chassis lol.
I have a 9700k in my desktop tower and getting over 70c is an accomplishment. That's like after an hour of gaming, and at that point the fans will be rather audible as I have them set to spin up pretty far if the CPU is approaching 80c.
One thing I wonder is how bad the thermals get when you have a 5700xt in the iMac. Mine has a beefy heatsink and gets very hot/noisy after gaming for a while (90-100c). I can imagine that thing frying a hole in the back of an imac chassis lol.
I know this is an old thread, but for the folks saying don't vacuum the iMac's vents: I just did it, and it seemed to help substantially. I have a 2020 iMac 27" with an i9 and 5700XT, so with the combination, it's definitely a bit thermally-challenged.
How I Cleaned My iMac
First, I unplugged the computer and placed it face-down on a flattened cardboard box. I took a toothpick and very gently ran it along the dust filter at the base of the iMac's chin. The intake holes that are machined into the aluminum chassis actually have empty space behind and between, so it's kind of like "flossing" out the bigger chunks. Then, I used a Dyson v11 cordless with a hard tipped crevice attachment, and after some light passes over the exhaust outlet at the back of the computer and over the intake vents in the chin, I managed to fill up about 1/5 of a canister with about 3 years' worth of dust.
How It Behaved Before
I noticed the machine would hit 100C sometimes in Intel Power Gadget just loading websites in Chrome. If I play Minecraft with any shaders that have basic water reflections, it would drop to 1FPS within 2-5 minutes, and in Activity Monitor, "kernel_task" would spike to use over 1,000% CPU (basically consuming all available cores). Some forum posts claim that's Apple's software management method to do last-resort thermal throttling by resource-starving other tasks.
How it Behaves Now
With all the dust out of my machine, it now runs at about 70-95C, in the extremes of either idling or running Minecraft with shaders, respectively. And "kernel_task" has thankfully not had to kick in, which was my main gripe as it made the system unusable (by design, supposedly).
Again, I think if you're careful about this and use an extension with a hard plastic tip and only hover the suction above the vent holes, the risk isn't too bad to damage the machine. If you're using a powerful corded vacuum on carpeted floors, you may have higher risk. It seems the 2020 iMac, with it's 10-year-old chassis and thermal design, isn't too well-suited for some of the higher end options in the final year before Apple discontinued it. The sensor and software calibration is very sensitive to any spikes beyond 100C at the CPU cores, and I have a feeling it was tuned specifically for a near-obstruction-free scenario with full airflow.
I think periodically cleaning it every year or so, depending on environment, is going to be a requirement to retain performance. I would even so so far as to say that although initial reviews of the 2020 iMac say it outperforms an iMac Pro, those were short-term reviews where dust probably wasn't a factor, since the Pro did have a better thermal design.
How I Cleaned My iMac
First, I unplugged the computer and placed it face-down on a flattened cardboard box. I took a toothpick and very gently ran it along the dust filter at the base of the iMac's chin. The intake holes that are machined into the aluminum chassis actually have empty space behind and between, so it's kind of like "flossing" out the bigger chunks. Then, I used a Dyson v11 cordless with a hard tipped crevice attachment, and after some light passes over the exhaust outlet at the back of the computer and over the intake vents in the chin, I managed to fill up about 1/5 of a canister with about 3 years' worth of dust.
How It Behaved Before
I noticed the machine would hit 100C sometimes in Intel Power Gadget just loading websites in Chrome. If I play Minecraft with any shaders that have basic water reflections, it would drop to 1FPS within 2-5 minutes, and in Activity Monitor, "kernel_task" would spike to use over 1,000% CPU (basically consuming all available cores). Some forum posts claim that's Apple's software management method to do last-resort thermal throttling by resource-starving other tasks.
How it Behaves Now
With all the dust out of my machine, it now runs at about 70-95C, in the extremes of either idling or running Minecraft with shaders, respectively. And "kernel_task" has thankfully not had to kick in, which was my main gripe as it made the system unusable (by design, supposedly).
Again, I think if you're careful about this and use an extension with a hard plastic tip and only hover the suction above the vent holes, the risk isn't too bad to damage the machine. If you're using a powerful corded vacuum on carpeted floors, you may have higher risk. It seems the 2020 iMac, with it's 10-year-old chassis and thermal design, isn't too well-suited for some of the higher end options in the final year before Apple discontinued it. The sensor and software calibration is very sensitive to any spikes beyond 100C at the CPU cores, and I have a feeling it was tuned specifically for a near-obstruction-free scenario with full airflow.
I think periodically cleaning it every year or so, depending on environment, is going to be a requirement to retain performance. I would even so so far as to say that although initial reviews of the 2020 iMac say it outperforms an iMac Pro, those were short-term reviews where dust probably wasn't a factor, since the Pro did have a better thermal design.
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