Assume everyone saw this story? It fixed my fans coming on with an external display attached to MacBook Pro 16" https://www.forbes.com/sites/barrycollins/2020/04/24/why-you-shouldnt-charge-your-macbook-pro-from-the-left-hand-side/#20caf84578ff
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That’s why I always kill -9 kernel_task whenever I see it 
(For anyone who doesn’t know: kernel_task is the “core” process of operating system; killing it would crash your computer.
If the kernel detects high a very temperature, it will attempt to cool the system by taking up a lot of CPU time but doing nothing with it. That makes it look as if kernel_task is consuming a lot of CPU and it makes the Mac feel slow and sluggish. In these kinds of cases, high CPU load by kernel_task is a symptom, not a cause of high temperature. (It’s worth noting that in some cases kernel_task can use a lot of CPU cycles for its own stuff and then also be the cause of higher temperatures. Virtual machine activity shows up as kernel_task activity, for example.))
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Have the same problem with my 16"mbp. Running two 27" dell U2719DC. Both monitors have USB-C but i’m running one with usb-c and one with hdmi-usb-C.
Haven’t managed to find any kind of solution to this. Tried using fan control in TGPro which worked pretty well, but even though the temps seemed to be within normal range, kernel_task started ramping up and would make the computer unusable.
When the monitor is not connected the laptop runs great, unfortunately I almost always use it at my desk. Hoping we have a solution soon as this is super frustrating.
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so i tried this one using switchresx and tried changing it to 55hz like i saw on a couple posts on macrumors… and it worked… at least for now.
temps are around 48-53 doing light tasks and fan speed is around 1700rpm (pretty much the same as when using the laptop without external monitor). will report back in a few days, but if you are experiencing this issue, give the resolution switch a try.
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Thanks for the information. What resolution are you running them at? I read somewhere that 4k is a multiple of 1080p, so to avoid scaling, I should run the display at multiples of that resolution ( 1x or 2x ).
Apple did another diagnostic system log capture session with me on 4/28 where they had me do 2 captures with different external display setups. I haven’t heard back from them yet.
I’ll try the lowering the frequency to 55Hz and see what happens. I came across that solution in my searches, too, but I haven’t tried it.
I’m still running in single display mode with aggressive fan settings via iStats Menu fan control. That’s keeping my CPU PECI temp under 70C for now. The temperature is normally between 60C and 65C with light usage.
I hooked up both 27" 4k displays and tried lowering the refresh frequency for both using SwitchResx. I tested them in tandem using the same resolution and refresh rates for each test.
3840x2160 @55 Hz - Overheat
1920x1080 @55 Hz - Overheat
1920x1080 @30 Hz - Overheat
So, no fix there, which was extra disappointing because my dual monitor arm kit showed up today. I reconfigured my desk with the arms holding both displays, hoping that the 55Hz trick would work.
I’m back to using a single display for now.
Updates. No fixes but I was able to overheat the Macbook with an external display and sidecar’d iPad.
5/3/2020
Apple Support had me create 2 more System log data capture files using their Capture Data utility.
1 was with 2 displays connected to the dock.
1 was with 2 displays connected directly to the Macbook Pro
5/8/2020
With these displays connected
1 External Monitor, U2718Q with Displayport to USB-C cable
1 iPad Pro 10.5" iOS 13.1 in sidecar mode with lightning cable
I was able to duplicate the overheating problem by playing a youtube Python tutorial video on the sidecar iPad.
The fans switched to high speed, around 4.6k rpm , temp 65C , and Radeon High End was at 20W
I moved the youtube video from the sidecar to my external display, and it Radeon power dropped to 7W and the fans eventually slowed down.
I was able to duplicate this once more, but after that I tried 2 more times, and could not duplicate it.
Also, I noted that my Macbook Pro won’t resume from sleep. I have to press the power button to boot it up every morning. After I log in, a crash port pops up and I send it. Power settings are at defaults, so I don’t think it’s a setting.
5/10/2020
I checked Apple’s return policy. Apple will honor return requests for 2 weeks after stores open if the return window expired while stores were closed for Covid19. Since I received the Macbook Pro on 3/27, after the stores had already closed, I can return it for a full refund.
With that knowledge, I ordered a Mac Mini to replace the Macbook Pro . It shouldn’t have the overheating problem, and I can finally focus on getting my business running instead of spending all of my time troubleshooting the overheating Macbook.
I should get in on 5/19. That will probably be my last post. ie everything works, no overheating, happy ending.
I got my 2018 Mac Mini last Friday and migrated my data and apps to it using the migration tool. It drives both of my external displays without any problems no matter what I throw at it.
Thanks to everyone who read and replied to this thread. This community is great.
My next post will probably be about how I purchased an eGPU and can’t get it to work, but let’s hope that day never comes.
Finis.
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I had this issue with my late 2018 15" MBP. I was using an LG 5K2K ultrawide connected on the left side of the MBP - this also charges the battery. Temperatures were usually mid 60s centrigrade. Occasionally the MBP would reboot instead of waking from sleep and once I saw that the temperature was 84C after one of these reboots. The wifi dropped a lot as reported in other threads and I thought it was a wifi issue but then I noticed this doesn’t happen to the other wifi devices in the house. So I switched the cable to the right. I just woke it from sleep and the temperature was 52C. It’s creeping up as I write, but seems to stabilize around 60C.
Last post on this topic, but not last post ever, we hope.
My 13" and 15" MacBook Pros have always worked fine connected to a 30" Apple Cinema Display. Pre-2016 models without USB-C. No fans, no excess heat.
I skipped the entire butterfly keyboard generation, luckily.
I now have a new 16" from work. The thing gets incredibly hot when connected to my 30". Fans often at full-blast. Random shutdowns.
It appears that any external monitors force the 16" to use the GPU? This is ridiculous. Feels like I need to downgrade to a 13" or Air to use the integrated GPU.
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For MBPs with discrete GPUs it has always been the case that any external display device forces the use of the dGPU. This is quite annoying when using something as simple as a projector while on battery.
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And here I am using an LG Ultrafine 5K and an LG 5K2K 34” together with my MBP running at 70-80 constantly and sometimes pushing 90-100.
One minor input. I have MBP 16 With i9 and 5500. If I keep the laptop vertical so that the heat can naturally escape from the back vents, then at idle the temperature is at 55C and the fans are at 1900-2000. I have Safari, Messages and MS Teams running. Adding Outlook, WhatsApp, Music, News, I get to 59C and 2300 rpms. Adding Photos it goes up to 61C and 2700-2900 rpms depending on how much work I am doing in Photos. So it seems that keeping the MBP vertical with the back vents up helps quite a bit.
Can you post a pic ? I am pretty sure I can picture the orientation you’re describing
Thanks
The MS Teams app uses lots of resources (both on Mac and Windows). You might want to try running it in a browser.
The fans on mine kick in whenever I use Teams, I imagine it is the culprit. The other applications that guarantee the fans will start up are chromium based browsers (Chrome/Brave/IE).
This is only while using the dGPU in the MacBook, if I use my eGPU the problem disappears and the system is silent even when using the aforementioned apps and a 4K external monitor.
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ikr… my max spec 2014 MBP 15 inch cant even power a bloody 1080p HDMi external display without the fan kicking and temperature rising… whereas my 2012 base model MBA 13 inch! Can 4 external displays including a 4K monitor without ANY FAN NOISE AND TEMPERATURE! What a bloody joke… this compulsory to switch to dGPU for the most mundane tasks…
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I have a 16" MacBook Pro with top specs except for the ssd got 2TB
I’m using dell’s U2520D 1440p monitor with HDR enabled my MacBook stays at 63C so I would say having two monitors running at 65C is normal its recommended to use USB-C
firstly it charges your Mac depends which display you got (mine delivers 90W to my Mac)
secondly its just neater and having less cables is a plus
getting an external GPU for a 16 inch macbook pro is useless your GPU is capable of running 5k monitors
I suggest you place your Mac on a flat surface with good air circulation
An eGPU is not useless for a 16”.
While it is capable of running 5K, the dGPU is still a mobile GPU. Running a desktop GPU is night and day better for anything graphics intensive and when you get used to it, the dGPU is noticeably slower even for productivity apps. For rendering video, it is more than double the speed. Even photo editing is faster and smoother.
In addition, when I only had the dGPU and one external 4K, the fan sound when on a videoconference was perceivable by people listening to my calls (it can be heard in recordings). When recording on Screenflow I could also hear the fans in the background. As soon as I plug in the eGPU this is solved. Then, it is completely silent even when rendering video at the same time.
It also acts as a hub for all my monitors, hard disks etc. So, I can connect multiple monitors, power and all my accessories with one cable.
Another advantage over the dGPU is that I don’t have to play games in 1080p to use high settings. I can now run AAA games on 4K and ultra settings.
It transforms the laptop into a fully fledged workstation.
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