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You are here: MacNN Forums > Hardware - Troubleshooting and Discussion > Mac Desktops > Hot iMac 20"

Hot iMac 20"
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Eldberg
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Dec 15, 2016, 02:47 PM
 
I have two old iMac 27" machines. The oldest one, from 2010, which has had it's hard drive replaced little more than a year ago, becomes very hot on the upper side. I'm wondering why. The other one which is from 2011, stays cool.

I thought there might be dust in some ventilation system so I vacuumed the hot mac underneath as well as on the top of the back, but no effect. What can be done?

Åke
     
P
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Dec 15, 2016, 03:35 PM
 
The vents are at the top, CPU on the left and GPU on the right. Is it just one side that is getting hot?
The new Mac Pro has up to 30 MB of cache inside the processor itself. That's more than the HD in my first Mac. Somehow I'm still running out of space.
     
Thorzdad
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Dec 15, 2016, 07:58 PM
 
Might be a fan has died in the hot one.
     
badidea
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Dec 16, 2016, 09:40 AM
 
Wasn't there some sort of problem with temperature sensors and HD replacement in iMacs? Could this have something to do with it?
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P
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Dec 16, 2016, 10:35 AM
 
Could be, but I don't think so. What happened there was that if you replaced the HDD with one that did not report the temperatures to the SMC in the right way (basically with one from another brand on the 2009-2010 models, and anything not from Apple on anything later), the fan that cooled the HDD and the PSU (the central fan) would go at full blast. Nothing ever got hotter. There were various ways to stop that from happening, including just getting a dummy to report that everything was cool and to not rev the fan. If that last happened and the Mac really needs the central fan to rev up, then yes it might get hot in the center, but it seems unlikely. HDDs don't produce much heat, and if the PSU gets hot for any reason, the iMac will just shut down as the caps fail.

No, the most likely thing is that either of the two cooling systems, CPU or GPU, has failed at some point. Fan failing is one option.
The new Mac Pro has up to 30 MB of cache inside the processor itself. That's more than the HD in my first Mac. Somehow I'm still running out of space.
     
Doc HM
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Dec 17, 2016, 06:00 PM
 
Over the years I have noticed a massive difference in heat thrown out by one iMac vs another of the same spec. One can be only slightly warm while an identical one can be oven hot.

As long as the hot one still works I would suspect it's just that.

There are various fan control apps that will report back the speed of each of the cooling fans and allow manual override if you want to see what effect on temperature spinning one of he fans up will have.
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Thorzdad
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Dec 18, 2016, 10:18 AM
 
My late-2009 21" iMac used to run whisper quiet until, at one point, I noticed one of the fans would start running hard whenever things got graphics-dense on the screen (a page full of animated gifs, Flash, complex Photoshop, etc.) I've come to assume that a sensor somewhere has stopped working correctly, and a ton of hot air comes pouring out of the top of the screen. But, as long as the fans work, I've decided not to worry about it. Now, if it was getting scalding hot with no audible fan noise, I'd be worried that a fan had died, which is a much worse problem, imho.

Dusting from time to time might help. I'd suggest using your vacuum hose to suck from the top as well as the bottom. I saw a video once of a guy who routed-out the top exhaust vents to be even larger, to allow more air to escape. He claims that helped the overheating quite a bit.
     
P
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Dec 18, 2016, 02:00 PM
 
Originally Posted by Doc HM View Post
Over the years I have noticed a massive difference in heat thrown out by one iMac vs another of the same spec. One can be only slightly warm while an identical one can be oven hot.

As long as the hot one still works I would suspect it's just that.

There are various fan control apps that will report back the speed of each of the cooling fans and allow manual override if you want to see what effect on temperature spinning one of he fans up will have.
There is a known variation that the amount of cooling paste applied varies widely, which would cause one machine to be hotter than the other.
The new Mac Pro has up to 30 MB of cache inside the processor itself. That's more than the HD in my first Mac. Somehow I'm still running out of space.
     
Eldberg  (op)
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Dec 20, 2016, 06:01 AM
 
I checked temperatures with te Mac Fan Control and the hottest place was 82 C. Most points registered as 42-65 degrees C. Turned out my daughter had turned the screen up to 100% brightness. That will of course increase heat.

Vacuumed the ventilation opening on the back (under the stand) and lowered the screen brightness. The machine is now running a lot cooler. Not as cool as the other one but no longer so hot that I am worried.

Thanks all who tried to help!
     
   
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