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Fan Control and Shutdown on Real iMac

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Joined
Dec 16, 2012
Messages
26
Motherboard
Z77x UP5 TH
CPU
i7 3770K 3.5Ghz
Graphics
geForce GTX 660 Ti
I've had hackintoshes for years (I have an i7 running el capitan that has run flawlessly 24x7 for over a year), and last year I bought a 5k because I wanted something compact with built-in speakers that didn't take up too much desk space. If you ever get that thought yourself, don't do it. It's the worst product Apple has ever produced.

The big problem is cooling and shutdown temperature; the thing insists on shutting down at > 90F (yes Fahrenheit). Apple is of course no help at doing anything other than re-installing the OS and crossing your fingers; they seem unwilling to admit that their product is fundamentally defective. So I'm hoping to get some guidance on how to tune the thresholds to stop it from shutting down until it actually overheats. It also "throttles" itself (the symptom is that it launches 100s of "kernel tasks" which suck up half of the cpu.

kernel_task.jpg


And no, it's not some monster application that triggers this. The fans will shoot up to 3600 RPM a few minutes after boot; I actually use a fan control app to slow them down.

Any guidance, help, suggestions, tuning tips, tools or anything to keep me from taking a sledgehammer to this thing would be greatly appreciated.
 
Joined
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Just had to look up what 90°F is in proper units... Okay, it's really not a lot. :lol:

Sounds like something completely messed up the power management of your iMac. Don't you have any warranty left? Personally, I'd return it to Apple and have them fix it, that's certainly not normal...
Depending on the GPU, the 5K iMac will usually go up to around 100°C (whatever this is in imperial units) until it starts throttling. And it should never have to shut down during normal usage...

Did you observe all sensor readings, maybe a single thermal sensor has failed?

Besides the common approaches (PRAM reset, SMC reset, clean install), I don't have any ideas left. I don't think its easily possible to tune the fan curve / shutdown thresholds, they're most likely burried deep inside the iMac's firmware / SMC.
 
Joined
Dec 16, 2012
Messages
26
Motherboard
Z77x UP5 TH
CPU
i7 3770K 3.5Ghz
Graphics
geForce GTX 660 Ti
I've run various diags and they all say everything is fine. I have TG Pro with also shows everything OK, and none of the temps are out of whack.

The big problem is that I'm not the only one with this problem; It's fairly prevalent. Numerous people have brought it back to apple, had them reload the OS and tell them that nothing is wrong. The general feeling is that Apple just doesn't want to fix it; it's probably software/firmware. The design is broken; there isn't enough air flow.

The late '15 imacs don't run as hot as the originals; it's a 65w cpu. 65C is about as high as it should go safely (71 max).

Apple will also insist on upgrading the OS, which will break a couple of things that I really need. I've upgraded El Capitan twice with no results so far. So I'd hate to jump through hoops for 2 weeks and then end up with a "sorry, we can't find anything wrong".
 
Joined
Dec 16, 2012
Messages
26
Motherboard
Z77x UP5 TH
CPU
i7 3770K 3.5Ghz
Graphics
geForce GTX 660 Ti
Just to follow up on this, I brought it in before my warranty was up and after 9 days of probing they found a bad sensor on the Display. Had to replace the entire display. I spend an hour with the genius (who was very competent) and picked his brain a bit. None of apples diagnostics found the problem, and the generation of kernel tasks to slow the cpu when a sensor tells the system that it's overheating can't be tunes or overridden in any way they'll divulge. Luckily the fan was spinning at 3200 RPM right away so there was no problem acknowledging that the unit needed repair.

Of course now I've revived my old GA-P55M system and got El Capitan running on it so now I have way more systems than I can use. Always good to have a spare.
 
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