I still don get it: what exactly is the problem? That the GPU reaches 108C under heavy load? So what?
As it has been stated numerous times (like from Andy 9l's last reply) this is a problem due the following facts:
1) On 105 C GPU goes to thermal throttle to cut down the heat. This means that it automatically underclocks from default 850Mhz to something like 720-760 MHz or even lower. This cut's down the GPU performance (I cannot estimate how much, but for some at least, maybe 15-30%). So you are not getting the performance you're paying for.
Reported stuttering side affects also suggests that oscilating GPU speed may cause these micro stutters. The GPU is not running optimally when it needs to throttle down, or change the GPU operating frequenzy constantly - nor it's not running by the specification customer's are expecting. If I am going to purchase m295X graphics with additional 250 $$$ I would expect to get promised 850Mhz, not 720Mhz.
2) With my own experience on building numerous PC gaming rigs I can say that no components are properly designed to handle over 100 C temps. AMD can say that their chips can run on 105C yes, but I am sure that this dramatically shortens the life span of the GPU, resulting numerous iMac 5k failures in a couple of years.
3) Also the reported temps between 105-108 C clearly suggets that even with thermal throttling the temps cannot be kept on 105C maximum (which is by the way the AMD's maximum operating temperature for Radeon based GPU chips, not even the recommended). This would suggest that, just I have linked the iFixit teardown images of iMac 5k's heat sink, it's just not built to dissipate such amount of heat this CPU + GPU combo outputs.
Also Running iMac 5K on 108C may cause failure even faster, maybe in couple of months. Yes, Apple care may take care of it, but it's still an extra hassle, and you may not have a computer for weeks. And what about those guy's who would like to plan owning these 3000k's machines more than 3 years?
Please stop spreading wrong theories. Just a quick look at the iMac's teardown shows without a shadow of doubt that iMac's case is not meant to be an additional radiator.
Yes, that is the case with the new iMac 5k 2014, but it may not be the case with the older macs that are getting hot on the back aluminium panel.
I believe that on the older iMac's which back panel get's hot, the thermal system has been designed the way that it conducts part of the heat to the aluminium chassis, which helps cooling the system passively resulting less noise as the actual fans don't need to start spinning so soon.
I believe Apple has "fixed" this due to some aestethics reasons (they must have thought that some users just think that hot aluminium back panel suggest that machine is overheating, while it actually just cools down the inner components when dissipating heat
)
So the design has gotten worse since.
Yeah I also remember reading that the actual amount of heat that is dispersed through the aluminum in a MBP is very small. The aluminum case of the iMac is not its heat sink.
Actually if you look any modern CPU or GPU heatsink you can see that all of them have copper heart (possibly with some liquid filled copper heat pipes) leading to ALUMINIUM heat sink.
The thermal properties of the metals goes so that conducting heat from another metal component (like the heat spreader of CPU/GPU) is more effective on copper than on aluminium, yes.
But when the heat must be conducted to air, there the aluminium goes stronger than copper.
So actually aluminium is a rather cood conductor when dissipating heat to air. Especially such large amount of aluminium that iMac's back panel is. It would be possible to passively conduct a large amount of the extra heat that iMac 5k is now suffering to iMac's aluminium back panel with just a few heat pipes. Why Apple hasn't done this, is just maybe the reason of aesthethics (that no one would feel that iMac runs hot, because the back panel is hot, which would actually make it run cooler
The fact that it remains cool is good. It means that most of the air inside the case is cool, while the hot one that passed by the CPU & GPU heat sinks is exhausted directly. This also protects other components and the screen from taking heat damage.
This just shows how little people actually understand about thermal conductivity, or generally electronics.
The same amount of heat is now trapped inside a very small area inside iMac's CPU and GPU segments causing a very large heat differences between processor units and surrounding components. This is fatal when these small areas constantly gets hot, and cools down, gets hot and cools down - causing failures to joints on the circuit boards sooner or later.
If the heat output (or at least part of it) was conducted to back panel of iMac, this would result - yes a hotter back panel - but also a passive cooling when the heat would dissipate to surrounding air on the outside of the iMac. This would also result lower GPU and CPU temps as well as more silently running iMac as the fan would not need to spin so hard.
Currently its just wrong that in the last generations of iMac the ability of the cooling system has been reduced but the heat ouput of the CPU and GPU has been increased. I would much rather take iMac 5k with such cooling system that conducts some of the heat to the back panel resulting less temps on GPU core.
