MacBook Pro (13-inch, 2017) fan go full speed and becomes loud when connected to a 4k external monitor

[factorial]

Hi.

I bought a new 32" 4K LG Monitor and I really like it, except that my MacBook Pro fans go crazy when the monitor is connected and it gets really loud as if I am running a high-demanding app or something, even when I just have 3 tabs open in chrome, or playing a youtube video in 1080p. I was checking a similar topic here: https://forums.macrumors.com/threads/16-is-hot-noisy-with-an-external-monitor.2211747/ But I couldn't really get a definitive answer/solution, and also it seems to be more about a different MBP model and setup.

My setup:

• Laptop: MacBook Pro (13-inch, 2017, Two Thunderbolt 3 ports), elevated using a stand for better ventilation.
• Monitor: LG 32UN650-W. 2560 x 1440 @ 60Hz. Connected directly to the laptop via CHOETECH USB Type C to DP Cable 4K@60Hz (‎XCP-1801).

Things I have tried:

• Reset the SMC.
• Updated the OS to the latest (macOS Big Sur: 11.3.1).
• Different resolution/scaling.
• Use screen mirroring instead.
• Enable/Disable HDR.

I attached a screenshot from IStat Menus that hopefully might help in a way to show what is going on? Does anyone know what could be causing this issue?

Thanks.

 

[Christopher Kim]

Sounds like you've got your laptop screen open as well, right? So your MBP is driving both the internal display + the external monitor (either in mirrored or desktop-extension modes).

Especially because you're driving the external 4K monitor at 2560x1440 (a non-integer scaled mode, which takes more horsepower because macOS pixel-doubles this to 5120 x 2880, and then scales it down to fit the 3840x2160 4K monitor), it's possible your MBP just isn't up for that without running the fans.

I would suggest try closing your laptop display and running in closed clamshell mode, and see if you still have the same issue. While laptop is closed, run the external display at i) 2560 x 1440 and see if fans spin up. If they do, then try ii) running external display again at actual 4K or 1080p (ie. exact 1:1 or pixel-double mode). If the fans don't spin up in either i) or ii), then it probably supports the idea that your MBP can't drive both your laptop display and the external monitor at the same time.

FWIW, I have a late-2016 13" MBP (the higher-end 4 TB3-port version), which I use in closed-clamshell mode, also into a 4K monitor that I run at 2560 x 1440. And for pretty much everything that I do, my fans don't spin-up and my experience is fairly smooth. But I also never have my laptop display open at the same time.

 

[Apple Knowledge Navigator]

Not much you can do about that, it's the integrated graphics. I have the same problem.

 

[factorial]

Thanks, Christopher Kim for your thorough explanation! I got the magic keyboard and trackpad 2 and connected it while having the laptop in clamshell mode as you suggested, and I can notice some improvement already. It gets even better when I use a native such as 3840 x 2160 or 1920 x 1080, which I believe works better for the reasons you mentioned.

The thing is, 3840 x 2160 is too small for me, and 1920 x 1080 is too big. I have no idea what resolution does people usually use for a 32" 4k monitor, but 2560x1440 seems to be a sweet spot for me, but I guess there is nothing much I can do about it? Except that I would have to upgrade my laptop (to M1 or something), which I was planning to do anyway by the next year or so, but until then, I just have to deal with it...