Dangerous CPU / GPU temperatures ?

[MortyMars]

IMO prior to doing anything else with your Mac you should try it with the existing apps disabled and running a cocktail of different challenging applications. My point being that the first thing to do is verify that one of your existing applications is not causing the problem.

Doing hardware maintenance (cleaning/repasting) may not be necessary if the problem is software.

Thanks for the advice.

As I indicated, I have quite a few demanding applications, which will therefore have to be tested.

What appeals to me, however, is that I have the impression that the problem always appears during a phase of rest or wakefulness...

 

[MortyMars]

Could be that air vents are clogged meanwhile you could use this app to increase cpu fan speed to lower the temp https://crystalidea.com/macs-fan-control/download

Thank you for the link, it's a good idea while waiting for the problem to be solved 👍

 

[MortyMars]

The foam piece, or anything similar, is essential if you are doing it on your own. Otherwise it's a "more than two hands" job to detatch and reattach the screen without damaging, chipping or cracking it.

Manhandling the screen is definitely the least pleasurable part of the process. The rest is fine.

I agree, I did this operation on a 21.5" and on a 27" it may be a little more delicate.
I will put my wife in hand 😉

 

[MortyMars]

The foam wedge is part number 944-4365, you can google where to find one.

The most important thing is not to insert a sharp metal cutting tool to get the screen off.
Only use the pizza wheel cutter, or a blunt plastic guitar pick.

If you poke anything in too deeply along the top you risk ruining the screen by slicing through the unprotected ribbon cable that runs close to the glass the full width of the top of the screen, to take the signal to the pixel matrix. 😱

Thank you for the reference and advice 👍

 

[MortyMars]

Thank you all for your advice and encouragement 👍

I am first considering going to the nearest Apple Store to see if they can help me, and at what price.
If this track gives nothing, then I will do the intervention myself because I feel quite confident and reassured by your advice.

As I said above, I am currently on the move and am therefore no longer in front of the problematic iMac.
But as soon as I return I will take care of this problem that upsets me a lot.
I will obviously keep you informed of my progress.

Warmly

 

[ignatius345]

Regarding the history of the SSD, I do not have it since it is a computer bought second-hand. So I don't know if it's the original SSD or if it has been replaced

DriveDx is very useful for assessing the health of a drive. It will show you how many read/write cycles it's been through, and what percentage of wear it's got left in it.

 

[Mrbobb]

I come from a PC world and in there, oftentimes there is a BIOS setting to run the system in Performance/Standard/Silent modes. Performance turns on the fan sooner/faster spin to keep temp low, Silent mode keeps the fan speed to its minimum to give noise priority over temp, and Standard is the middle compromise.

Don't the Macs have similar settings?

 

[Mrbobb]

Doing hardware maintenance (cleaning/repasting) may not be necessary if the problem is software.

I make the assumption that the hardware will auto-throttle when the software mis-behave.

 

[uacd]

If you used your Mac extensively in very dusty environment then it could have clogged air fans. You can try to stick vacuum cleaner to air vents to get some debris out. However it might be not the issue. I suspect your GPU is dying and macOS naturally redirects some tasks to CPU. Since yours is Radeon Vega, I highly suspect that. These were some of the faultiest cards back in the days and I believe Apple even had replacement programs, just for Mac Pro, not iMac. It is worth to get it to Apple service or try to find some software hacks to disable GPU completely

 

[Romain_H]

Any temps near 99c is not a good thing, regardless of the specs of the computer. If you didn't have these temps a few months, or even years ago, then, something changed internally with your computer.

You're computer is 6 years old, there's number of possible contributing factors leading to increased temps. The thermal compound has gotten old and less effective. Re-pasting may benefit the computer both the CPU and possibly the GPU. Dust infiltration, dust is an insulator and could be impacting how well your fans are able to cool the internals. Fan malfunctions, maybe the bearings or fans are not running optimally anymore.

That is incorrect, sorry to say. CPU specs state a design temperatue of 100 centigrade. Those temperatures alone are not cause for concern.

If the temperatures have been lower and only recently started to rise to 100 C it might

 

[maflynn]

That is incorrect, sorry to say. CPU specs state a design temperatue of 100 centigrade. Those temperatures alone are not cause for concern.

I was waiting for someone to say that - there's always one in the crowd to defend the 100c mark. Don't forget if the cpu is near 100c, then its really toasty on the other internals which are a lot more sensitive to the heat, such as the VRMs, SSDs, etc.

Its generally acceptable to deal with spikes of 90c and above, but not constantly at +90C

What is a normal temperature for a CPU?

However, while the occasional spikes of peak temperatures to 194°F (90°C) are okay in isolated bursts, prolonged exposure can impact performance, and even damage the longevity of the chipset over time.

Safe CPU Temperature Range: What Temp Should My CPU Be?

As a generalization that might help you identify a serious problem, a CPU core temperature that is consistently going over 45- to 50-degrees Celsius while idling is possibly a cause for concern and a temperature that is consistently going over 90- to 105-degrees Celsius while under full load is probably a cause for concern (depending on what CPU you have).

 

[Romain_H]

I was waiting for someone to say that - there's always one in the crowd to defend the 100c mark. Don't forget if the cpu is near 100c

Because it is true. Repeating unqualified hearsay is still hearsay

 

[maflynn]

Because it is true. Repeating unqualified hearsay is still hearsay

Its a fact that electronic devices degrade and the life span is shortened the longer its exposed to high heat. Whether you care to believe it or not, is of no concern of mine. I see no further reason to continue this debate, so I would just say have a nice day

 

[MortyMars]

DriveDx is very useful for assessing the health of a drive. It will show you how many read/write cycles it's been through, and what percentage of wear it's got left in it.

Thank you for the link to this tool that I did not know.
I will test the SSD of the problematic iMac to see if it is a track to remember 👍

 

[MortyMars]

I come from a PC world and in there, oftentimes there is a BIOS setting to run the system in Performance/Standard/Silent modes. Performance turns on the fan sooner/faster spin to keep temp low, Silent mode keeps the fan speed to its minimum to give noise priority over temp, and Standard is the middle compromise.

Don't the Macs have similar settings?

I don't know such a system feature on Mac.
But there are third-party tools (mentioned here by the way) that do something very similar.

 

[MortyMars]

I make the assumption that the hardware will auto-throttle when the software mis-behave.

It's a possibility indeed...

 

[MortyMars]

I suspect your GPU is dying and macOS naturally redirects some tasks to CPU. Since yours is Radeon Vega, I highly suspect that. These were some of the faultiest cards back in the days and I believe Apple even had replacement programs, just for Mac Pro, not iMac. It is worth to get it to Apple service or try to find some software hacks to disable GPU completely

I hope this is not the case because it would be catastrophic in terms of cost, or even repairability 🤕
Is there a way to test the viability of your graphics card?

 

[MortyMars]

That is incorrect, sorry to say. CPU specs state a design temperatue of 100 centigrade. Those temperatures alone are not cause for concern.

If the temperatures have been lower and only recently started to rise to 100 C it might

In fact, I am pretty sure that untimely restarts and shutdowns of the machine are not caused by overheating, because as I indicated they appear during phases of low CPU/GPU load, or even during a normal standby or maintenance.
The temperatures I indicate are those at almost full load of the CPU + GPU under X-Plane 12 (a flight simulator for those who do not know).
I came to do these tests because this kind of problem immediately makes you think of a material overheating problem.

 

[uacd]

I hope this is not the case because it would be catastrophic in terms of cost, or even repairability 🤕
Is there a way to test the viability of your graphics card?

Try to run diagnostics as explained in the first comment here.

Start your Mac and hold whichever combo works:
- Option + D (Early 2011 and newer; Mountain Lion tested)
- Command + D
- D

 

[MortyMars]

I was waiting for someone to say that - there's always one in the crowd to defend the 100c mark. Don't forget if the cpu is near 100c, then its really toasty on the other internals which are a lot more sensitive to the heat, such as the VRMs, SSDs, etc.

Its generally acceptable to deal with spikes of 90c and above, but not constantly at +90C

What is a normal temperature for a CPU?


Safe CPU Temperature Range: What Temp Should My CPU Be?

Thank you for your analysis and your references
I admit that I am not very reassured by these temperature rises close to 100°C.
At this very moment, I am on my second iMac, identical to the first with the amount of RAM, and under the same test conditions the temperatures reached by the CPU and GPU are about 5°C lower.
But it's also a little cooler where I am now.

 

[MortyMars]

Try to run diagnostics as explained in the first comment here.

Start your Mac and hold whichever combo works:
- Option + D (Early 2011 and newer; Mountain Lion tested)
- Command + D
- D

Thank you, but isn't this a procedure specific to the MacBook Pro range?

 

[uacd]

Thank you, but isn't this a procedure specific to the MacBook Pro range?

It should work just try and follow the steps when tool runs.

MacOS usually has same commands for all devices, I’ve also checked - it must work on any Mac

 

[MortyMars]

@maflynn @Romain_H,

I appreciate the help you both seek to provide and I thank you for it.
I think there is some truth in both speeches and that is what will encourage me to do what is necessary, measuredly, to make this computer that I love last, even if perhaps it means limiting it to less demanding tasks.

Thank you and all the contributors to this post 👍

 

[MortyMars]

It should work just try and follow the steps when tool runs.

MacOS usually has same commands for all devices, I’ve also checked - it must work on any Mac

OK, thank you.
Here is one more interesting test that I will be able to do on the patient 👍