I suspect that a resolution of this problem will only be finalized when folks fully report the following specifications:
the size + resolution of the external monitor
the processes, memory, and graphics specifications of the 16in MBP
the type of adaptor and other peripherals connected
I drive a 27in Quad resolution monitor through an Anker thunderbolt to HDMI adaptor on my 2.4 GHz 8-core i9 with 32GB RAM and the AMD Radeon Pro 5500M 8GB graphics upgrade option. I have a USB-B 7-port hub attached to the adaptor with a USB-2 keyboard and a USB-2 trackball on-line. I occasionally run a USB-C external drive for Time Machine backups. I can have some intensive ongoing analytical operations with one piece of computational software, and I otherwise typically do extensive composition work in LaTeX, development work in Curio, and tracking with OmniFocus. I also run Zoom sessions with my iPad connected over AirPlay.
I have had none of the problems that folks are mentioning with highly excessive fan speeds / noise. I do have my MBP on a mechanical-run fan cooling platform, especially during intensive work (mostly always).
I’m in the same boat as you guys and I was struggling with extremely hot MacBook Pro 16" (up to 70ºC/158ºF) with two external monitors connected. Today I’ve managed out how to fix that (at least for my setup) and wattage of the Radeon GPU dropped from 20W to 5W and tº from 65-70ºC/140-158ºF to 50ºC/120ºF just by setting the refresh rate of my 2xFullHD monitors to 55Hz (the default one was 60Hz). I’ve used SwitchResX for that.
Settings for SwitchResX:
Steps are simple: create a new custom resolution for each monitor and set two parameters: GFT and Vertical scan rate to 55 (your value could depend on what your monitor is supporting). Save and reboot.
For some reason, the app is complaining that settings were not applied though they are.
I can be wrong but I guess it’s sort of a bug in drivers caused by some standard refresh rates which leads to extensive power-draining by discreet GPU.
Hope this will help you.
PS: photo of my setup with a description will be in the next post as far as new members can’t put more than 2 images per post.
I am using a 2017 Macbook Pro with touchbar model. All these 4 years, I have wasted giving my macbook to multiple service centers and getting the logic board, display board and battery replaced multiple times and still, Apple doesn’t have a solution.
It gets too hot(uncomfortable to even type) when connected to an external display. I have tried multiple dongles and cables, tried connecting to multiple monitors(Dell, HP, LG, BenQ) and still the issue is the same. Due to the heat, the battery drains in less than 2 hours. Have tried using external cooling pads, and not much gain.
Without any external monitors, it delivers 8 hours on battery.
For me, there was not - other than selling it. My experience with two LG 5K displays attached was that the fans (it was a 2019 MacBook Pro16 inch with an i9 processor, 64gb of ram, and plenty of storage) would spin up almost immediately and would continue until I unplugged from both displays. Could not be resolved with Apple or anyone else.
So, I sold it, stored one display, stashed most of the money, bought the cheapest M1 Mac mini, added a OWC Thunderbolt hub and a 2 Tb SSD. Very satisfied with the setup (until the new 16 inch MacBook Pro comes out, of course).
Based on all the comments above which have been really helpful in debugging this; I did some playing around with my MBP 16" in clamshell mode and refresh rates for my external monitor (ASUS TUF Gaming VG27AQ).
What I found I thought was kinda interesting which is why I’m posting here. At some refresh rates, I get much higher idle Radeon High Side Wattage ~18-21W vs. ~6-8W. Initially I thought this would naturally go up as my refresh rate went up, but interestingly at 59.88Hz I also get the higher power usage.
Here’s my full results (I didn’t take multiple samples or test different monitors so take these as anecdotal numbers for my particular setup). Resolution was always 2560x1440 with HDR off and the Macbook was in clamshell mode. Here are my display settings for reference.
If anyone is wondering whether those wattages fluctuate, here’s a graph of iStat menus which shows that yes there is some fluctuation of the Wattage as I do different things but for the most part the baseline wattage stays much lower when I pick one of the better refresh rates above. The big spike happened when I opened up a game with smaller spikes for youtube videos and other GPU related tasks.
In the middle important work video call today, I had to disable my external screen due to heavy throttling (kernel_task at +1000%), itself due to combination of high GPU wattage and high room temperature. Extremely disappointed with the MBP16, and I hope the issue is a buggy driver, not Radeon hardware - otherwise there is no real hope.
I’m also having this issue across multiple machines - all very modern. Anyone got any ideas? I can see that plugging in the external forces the radeon card to activate and this seems to cause the issue. Not all the time, but often
Installed Monterey public Beta yesterday. I’m around 16W for the GPU, down from 20W. This still is short term but it seems like an improvement. Fans still too loud to use the laptop mic for call through.
Hey, couldnt follow the thread all the way to the bottom, so not entirely sure if the issue has been fixed, but here is my two cent - Why I RETURNED my 4k monitor // MacOS Scaling Explained! - YouTube
You can refer to this video where he nicely explains how the Mac is using GPU to do the scaling if the resolution of your monitors are not 220 PPI or 110 PPI. Maybe the resolution settings can be checked to reduce load on your Mac. Let me know if this helps!
I have a 14" MBP with an M1 Max (32 GPU cores) connected either to a pair of 4K displays or a Studio Display and I almost never hear the fans at all. If I do hear them, it’s something that I have to double check by listening closely just to be sure that it’s the Mac and not something else in the room. This only happens during moderate to heavier workloads or on very warm days.
I don’t usually push all of the CPU cores at once, so I can’t tell you how it sounds under very heavy workloads, so I can’t comment how loud the fans can get.
For comparison, I also have a 16" MBP that is connected to those two 4K displays and it runs its fans much more audibly than the 14". The same workloads will make the that machine’s fans relatively loud. Even light work will make the fans become audible, but I don’t see the behaviour whereby just driving an external display makes the fans spin up.
I am comforted that the M1 MBP fan does not run when connected to external displays. Currently, I own an M1 Air and as it is fanless, my computing life is so blissful. I do not want to go back to intel Macs, or any Macs that have fans. That’s why I’d be concerned if the M1 MBP fan starts firing up when connected to external displays, as the intel MBP fan will surely do. In the days before M1, the intel Mac’s fans will blow continuously and all I have are Safari, Outlook, a few Office documents and Webex session, all connected to an external display. It drives me crazy.