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My MBP15" often overheats (forcing fans to full) when plugged into my LG 5K Ultrafine. I understand that it runs at 60Hz and that this puts strain on the GPU. Since I'm mostly coding/browsing I wanted to test out 30Hz to see if it reduces the heat levels, but I don't see any way to control this in the UI. Is this some hidden advanced menu or CLI method?

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Clarification: My machine is not shutting down, so Apple's fan speed logic seems to work fine in my case. I'm looking for ways to reduce the heat output so that high fans speeds are hopefully not required at all.

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  • Define "overheats". Does it shut down, or does it just ramp up the fans?
    – benwiggy
    Commented Jun 10, 2020 at 8:09
  • Try to open with Ctrl + Click the monitor preferences to see all the configurations available.
    – Matteo Guarnerio
    Commented Jun 10, 2020 at 12:01
  • Added a clarification about overheats: it's just that the fans climb to "runway speeds" but no crashes due to heat yet.
    – Nic Cottrell
    Commented Jun 10, 2020 at 16:44
  • No idea, but I think there were some laptops which always used the dedicated GPU instead of the Intel integrated GPU when a certain resolution was exceeded. Is there a way to force a Macbook to use the integrated Intel GPU?
    – Michael
    Commented Jun 10, 2020 at 17:27
  • @Michael there’s no way to do that. MacBook Pro with TB3 ports hardwired to use discrete GPU card on those ports.
    – Alexey Kamenskiy
    Commented Jun 11, 2020 at 11:36

4 Answers 4

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It's not possible to change the frequency and the physical resolution of this display.

IMHO changing that will not lower the thermal load of your MBP, because once you connect an external display the "external" GPU will be used and it has at least 10W of consumption. This is very apparent in the newer 16" MBP, where I measured ~20W of base load with no matter how many or what kind of monitors are connected.

edit: You can change the resolution (by option-clicking the Scaled label) or control-clicking Display preferences to show additional resolutions), but (at least on my setup) it barely makes any difference.

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According to the monitor manual, the monitor itself does not support 30 Hz.

In the section regarding "Signal Timing" they only list 60 Hz as supported. In the product specification sheet, they write that the vertical frequency can be 48 Hz to 60 Hz.

Therefore I do not think 30 Hz is achievable with this monitor.

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As addition to the other answers - changing monitor refresh frequency will do nothing in this case (I.e for some TB3 external monitors that would allow that)

Monitor frequency defined on monitor and as driven by monitor hardware. The heating of your MacBook comes from discrete video card that is used to communicate with external monitors. And it heats up due to new MacBook Pro poor heat dissipation design. Which has nothing to do with monitor refresh frequency.

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  • Every CPU and GPU has had power saving features since decades back, especially for mobile use, so it makes sense that refreshing the graphics at half the speed would allow the GPU to enter sleep modes or to selectively downclock itself more often.
    – pipe
    Commented Jun 11, 2020 at 11:20
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    @pipe there’s significant difference between monitor refresh rate and signaling frequency. It is not the same thing. While in old CRT monitors the signaling frequency and “refresh rate” were directly related in modern monitors they are not. You are correct there are power saving modes for GPU and CPU. But that has nothing to do with monitor refresh rates. To put it simply old CRT (I.e. VGA) are analog signals they literally send every pixel, modern is all digital and monitors have their own embedded controller that decides how to draw the picture and talks back to your computer.
    – Alexey Kamenskiy
    Commented Jun 11, 2020 at 11:26
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This question looks like an XY problem, so I'm not going to address monitors at all but instead how to fix your overheating problem in the first place.

Apple laptops do not like to use their fans. Usually, the only reason they overheat is because the fans don't turn on soon enough. If your fans are running at full speed with the Apple fan curve (which hates to turn on the fans), this is a very bad sign.

The solution to your overheating problem is to turn the fans on sooner. There will be more noise, but your laptop will not overheat. You can do this by using an app like Macs Fan Control to run the fans at full speed before overheating happens. I've run extremely heavy loads on my laptop, including running multiple games at once, training a neural network, and rendering complex scenes and it has never throttled, not once, except in cases where I forgot to turn up the fans.

If you want to avoid all fan noise however, then I've got bad news. Apple already tries to avoid fan noise, and by doing that they starve the laptop of the cooling it needs and drive it to thermal throttling.

If you want to prolong the life of your laptop, I would recommend getting used to the noise (it's really not that bad). Overheating can damage critical components including the CPU and GPU themselves.

And especially if you have a newer laptop, any broken parts can mean a total replacement, and your data gone. Better safe than sorry.

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  • In fact I use the exact same apps to do the same work - just sometimes in my kitchen with no external display, and something with a 5k external display. Within about 5 minutes of the display being plugged in fans start up. So forcing them up earlier will not help me at all.
    – Nic Cottrell
    Commented Jun 12, 2020 at 21:14
  • "Within about 5 minutes of the display being plugged in fans start up. So forcing them up earlier will not help me at all." Explain? If you turn them on earlier, your machine will not overheat. But if you try to stop the fans from turning on then your machine will straight up shut down as soon as it reaches critical temperature
    – Dev
    Commented Jun 13, 2020 at 1:03
  • Agree with approach. I have tried smcFanControl and Macs Fan Control, and found TG Pro (commercial) the best tool for me - it lets you define the temperature at which fan will move to certain level, and has nice features like showing current temperature and RPM clearly on menu bar. I don't have an external GPU but this is supported and I think TG Pro could automatically ramp up fan based on GPU temperature, as well as CPU.
    – RichVel
    Commented Jun 13, 2020 at 10:42
  • For those who desire fan curve control, TG Pro looks like an attractive option. It helps lessen the burden if you don't want your fans on full speed 24/7, but still want them to turn on sooner to prevent overheating. That said, it is paid. While $10 is a fairly good deal, I personally prefer Macs Fan Control anyway as it is free and also works on Windows (important for Boot Camp users)
    – Dev
    Commented Jun 13, 2020 at 14:03

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