1

I have a 2014 Mac mini with an Intel Core i5 processor. I noticed that no matter how much I used it, the fans barely ramped up. Using iStat Menus I noticed that it would usually stay around its base speed of 1800 rpm (0% of the fan speed range), and go up to 2000 (7%) rpm under heavy load. It would never reach the maximum of 4845 rpm (100%) unless I manually set it using iStat Menus.

To stress test the CPU I tried running 16 instances of yes > /dev/null &, play an 8K video on YouTube, and compress a video on Handbrake. Definitely more than necessary but my fans still didn't ramp up after a few hours of testing. This is what my stats looked like during the hour that I checked in with it:

General temperatures, power usage, fan speed, and other stats:

CPU Usage (left) and fan Speed, around 2000 rpm (right)

cpu usage fan speed

Power usage, hovering around 28W:

power usage

What's quite surprising is the thermal limit, it seems like it doesn't want to go past 85°C whereas every other Apple CPU I've seen gets close to the max junction temperature (usually 105°C) before the fans start kicking in to keep it from throttling.

One suspicion I have is that for some reason my CPU is being throttled or underclocked for some reason. If so, how do I prevent this from happening?

4
  • I'm not entirely sure I understand the question. Is it about overclocking your Mac Mini? If so, can you confirm that throttling is actually happening? Or are you looking for a way to control the Mac Mini fan? If so, have you found applications so far that might work? Jul 12 at 16:04
  • 1
    Thanks for the comment, I edited my question to be a bit clearer. Essentially I'm confused why the CPU never goes higher than 80°C and why the fans never go beyond 2000 rpm. With all the Apple devices I've ever owned, both new and old, the fans will go to 100% if you stress it. Except perhaps the M1 MacBooks. Jul 12 at 18:05
  • Have you checked if the CPU is being throttled for thermal reaons? And if you use a fan control app (like iStat menu) to manually increase the RPM, does the performance increase? Jul 12 at 18:14
  • 2
    It's a 2-core i5 CPU, in a box that's designed to cool 4-core i7s. I would focus on whether you think the performance is up to expectations, rather than what the fans are doing.
    – benwiggy
    Jul 12 at 20:12
1

... but my fans still didn't ramp up after a few hours of testing.

The slow fan speed ramp-up is by design. As the CPU crunches data and heats up, the Mini will not immediately increase the fan speed. Instead it will wait for sometime to allow its metal body to act like a secondary heat sink and absorb some of the heat. And only after that will it slowly increase the fan speed to further cool down the CPU.

Personally, I've felt that the default Apple settings for heat management, while really ideal for the majority use cases on Mac, aren't the most optimal when you really want full CPU performance. One of the things Apple's marketing likes to highlight is that the mac is "quiet" and you can "barely" hear the CPU fan. So to meet this design need of "quiet and thus less distracting" computers, I feel they do resort to more CPU throttling than necessary, and a slower ramp of the fan speed to reduce the fan noise, at the slight expense of CPU performance. (This is more true for the Apple laptops than their desktop counterpart though, unless you have made custom modifications to your desktop Mac).

(Note: Be careful in messing with the default fan speeds and / or CPU voltage settings to overclock the CPUs. It can reduce the life of the CPU fan and the CPU and in worst cases even damage it. And Apple parts and repair costs are very high.)

One suspicion I have is that for some reason my CPU is being throttled or underclocked for some reason. If so, how do I prevent this from happening?

Even I find it hard to believe that your CPU doesn't cross 85 degrees with what you described. Though, I do have a doubt if you are stressing your CPU enough. The Youtube video maybe being decoded by the hardware decoder in the CPU. If you use a hardware encoder (VideoToolbox) on Handbrake the encoding will be done by the hardware encoder on the CPU, and not by the CPU cores.

One way to really use all the CPU cores fully, for a while, would be to encode a movie using x265 / HEVC encoding. HEVC encoding is very CPU intensive and is a good way to stress your CPU.

Open any 720p or above 1+ hour long movie in Handbrake. In the Video tab, choose H.265 (x265) in the "Video Codec" drop-down menu. Choose a Quality / CRF of 18. And most important, set the encoder / H.265 "Preset" to "veryslow". Now start encoding.

This should easily use up all the CPU cores to 100% and in just 5-10 minutes cause the CPU to touch 100 degrees at room temperature (28 to 35 degrees here).

If that doesn't happen, it's a good guess that some CPU throttling is happening.


Intel Power Gadgets

The Intel Power Gadgets app is very useful for more accurate monitoring of the CPU while stress testing it.

It also has built-in test suites to test both the CPU and GPU

To run the tests:

  1. Open Intel Power Gadgets.
  2. In the Test menu, select All Thread Frequency under CPU Tests.
  3. In the Test menu, select Maximum Frequency under Intel Graphics Tests.
  4. A check mark will appear on the selected menu item and the tests will start.
  5. To stop the test, open the Test menu and click again on the menu item with the check marks. The check mark will disappear and the test will stop running.
3
  • It's also kind of surprising to me. After running for 10 minutes the PECI temperature still does not cross 87 degrees, even at base 1800rpm speed. I even have a Thunderbolt dock on top of the Mac mini which does not help with the cooling. Here's what I see on Intel Power Gadget. From what I can tell it's clocking in at 2.4 GHz although the processor should be capable of turboing up to 2.7 GHz. Strange that it's not overclocking automatically despite running so cool. I'll try using Volta to see if I can boost it to 2.7 GHz. Jul 13 at 23:44
  • From your screenshot, Core REQ 2.7 means macOS requested 2.7 Ghz from CPU. But as Core MAX 2.5 (maximum frequency so far) and Core AVG (average CPU frequency) 2.4 shows, CPU is only running at around 2.4 Ghz. That is normal and can happen when your HDD cannot supply data fast enough to the CPU to process it. A faster SSD can help here. (By the way, I forgot to add that you can stress test the CPU through Intel Power Gadget too - please see updated answer for more info).
    – sfxedit
    Jul 14 at 1:17
  • Thanks, that actually managed to ramp up the fans and the CPU temperature much more. Got this. For some reason the core is maxed at 1.7, I assume because the GPU was being utilized heavily, so the CPU had to be downclocked. But I have no idea Jul 14 at 3:02
4

What the OP has effectively demonstrated is that Apple's extensive efforts and expenditure towards building out a thermal management solution that covers the entire performance envelope have been successful. The Mac is behaving precisely as it was designed to: By applying the least amount of active cooling necessary to maintain safe operating temperatures at any given load. There are multiple whole teams at Apple whose entire job description is to make this a reality.

As others have said in the comments, you may not even be able to induce a sufficiently high load to exceed your Mac's active cooling capacity and force throttling in your current environmental conditions. In order to test that your machine will, indeed, spool up to a 100% fan duty cycle, you will need to place your device in a container with as little ambient airflow as possible and let your load run a while. At some point you will notice the fans at max and the die temps rising and the throttling kicking in, eventually followed by an emergency thermal shutdown.

3
  • I don't know why but this design choice, although it makes perfect sense, seemed incredibly strange to me, which is what led me to ask this question in the first place Jul 13 at 10:23
  • 2
    Also, another case of "Looking at iStat makes you worry about normality." ;-)
    – benwiggy
    Jul 13 at 10:39
  • While Apple does have some great engineers, and does focus a lot on efficient thermal management in their devices, Intel CPUs are also a factor here. Intel made some good strides in reducing the power consumption of their CPU thus reducing the heat produced by it while also increasing battery life. (E.g. Apple advertised 7 hours of battery life for the 2012 13" macBook that used Intel Ivy Bridge CPUs. But later 13" macBook models that used the Intel Haswell processors were advertised as offering 12 hours of battery life. Later intel Broadwell CPUs were said to be 10-15% more efficient.)
    – sfxedit
    Jul 14 at 1:29

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .