Level 1

7 points

iMac 5k i7 cpu hits 100 °C regularly

I recently bought the 5k 27" i7 iMac. When the cpu is idle it stays in the low 30s, when under moderate load (HD movies, internet, Photoshop etc) it doesn't really get over 50 °C, but when I use it to render stills/animations in Cinema 4D (or After Effects) and all 8 threads are being utilized the temperature stays almost constantly at 95 °C and regularly peaks at 100 °C! At this point the fan is louder than my vacuum cleaner, the frequency drops but the temperature never does. I did a test render for about an hour and the fan never managed to cool down the cpu under 90 °C, even if the frequency dropped from 4 GHz to about 3.8. I used Macs Fan Control and Intel's Power Gadget to monitor what is going on and got the same readings.

I don't think there is anything wrong with the cpu as it cools down to 45 °C in a matter of seconds after I stop rendering. The fault is (I guess) in the iMac's cooling system, since it uses the same heat sink for both the cpu and gpu (which by the way also gets over 90 °C after a few minutes of doing virtually nothing in Civilization V), and has to cool them both down, and the power supply, and the rest of the components all squeezed in a space smaller than some laptops have with only one fan.

My question is: how worried should I be? I don't think it is either normal or acceptable for the cpu to be at such high temperatures for longer periods of time. I don't do rendering every day, but I will do at least full 48 hours of rendering per month and having the cpu hitting the 100 °C mark every few seconds really doesn't sound right to me. Or am I just over reacting and it is perfectly normal for the i7 to operate in the 90+ range all the time?

iMac with Retina 5K display, OS X El Capitan (10.11.4)

Posted on Apr 11, 2016 9:27 AM

19 replies

MichelPM

Level 10

81,535 points

Oct 1, 2016 3:30 PM in response to BSD Guru

I use a small 7' inch diameter , 2-speed Vornado fan on the back of my iMac.

You do not a huge size external desktop fan to cool the back of your iMac.

Vornado, also has a 9 inch diameter fan with 3 speeds which I am thinking about switching formthe back of my iMac.

https://www.amazon.com/dp/B00D8NZ85I/ref=wl_it_dp_o_pC_nS_img?_encoding=UTF8&col id=20AIQPDUUWU9G&coliid=I2UFSK9YDS1DP6

It runs not too loud and does a good job of circulating the air and dispersing it from the back of my iMac.

Been using this for years on my 2009 iMac which gets incredibly hot, too!

You don't need to drill holes, just keep the back cool.

Aluminum is a good conductor of heat, but does a poor job of convecting the majority of that heat away from the iMac.

The heat issue used to be worse when Apple was making the iMac casing in earlier models in plastic, but those models had more than one fan AND Apple added more ventilation holes in the back casing of the iMac that allowed a lot more of the heat to more easily escape.

It, also, helps to identify on the backside and or top of the iMac where it gets the hottest and place the fan behind the iMac on the left or right side of the stand that gets the hottest.

On the older aluminum iMacs, looking at the iMac from the fronts, the left rear side and top is where my iMac gets the hottest.

MichelPM

Level 10

81,535 points

Mar 24, 2017 9:41 AM in response to imac27i7

There is no real resolution.

If the heat from your iMac bothers you, as it does, myself, as I have already stated numerous times, run a small variable speed desktop fan on the back of your iMac.

In addition, install a software fan control to manually ramp the iMac's internal fans up and down, if needed, to compensate for what I feel is excessive internal heat.

If you use a software fan control, be careful not to ramp up the fan speeds too much causing the fans to act more like a vaccuum sucking in more outside dust, dirt, lint and to avoid premature burn out of the iMac's internal fan motors.

Been doing that for years!

Keeps all of the iMac's internal temperatures down and the back of iMac cool.

Fairly cheap solution.

A cooler running Mac will last longer as you won't be "slow roasting" internal components.

Good Luck to You!

Versagious Author

Level 1

7 points

Oct 28, 2017 4:27 PM in response to imac27i7

Hey, it's been over 6 months since your post (and it's probably too late), but i never really resolved the issue. The cpu still gets hot enough to boil water whenever I do video or cgi rendering - or anything that uses full cpu power. The rest of the time everything works fine. I never took the iMac back to the store to have it checked, they said they will have to send it to Vienna (their repair shop location) and the whole thing could take up to 3-4 weeks, and I never found a month of time to spare. As Apple announced the iMac Pro with two bigger fans 😉😉 I think there is nothing one can do with the i7 iMac, its just not really aimed at the "pro" market.

My solution is to render at night when I am out of the office, I still have a year and a half of Apple care left and if the cpu melts trough the aluminium, well, I guess I get a new iMac! I will sell it a few months before the Apple care expires though, I don't expect it to last 9 years as my old iMac did. I have a Macbook air and its all I need for internet and answering mails, as for work ... as BSD guru suggested I will probably build a hackintosh. I haven't tinkered with a PC in like 15 years and it actually sounds quite fun to do that again! The new iMac Pro will be just too expensive and frankly I don't trust the current iPhone focused Apple to build a proper machine. It's a shame, since it was graphic designers and people involved in desktop publishing that were the only ones buying their products when they were one step from becoming a footnote in history.

Anyway, not to make this into and old man rant: if anyone else is having this problem - post your cpu temperature madness, who knows, it might help someone make a more informed decision before buying the i7 5k iMac. Also if there is a solution to this problem, please post it - I would love to be wrong about the iMac, and will wholeheartedly apologise to the almighty corporation.

MichelPM

Level 10

81,535 points

Sep 30, 2016 8:47 PM in response to BSD Guru

Get an external desktop fan to start cooling down your iMac from behind.

This was my only other solution for keeping iMac heat issues at bay.

Good Luck!

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iMac 5k i7 cpu hits 100 °C regularly