MacBookPro 16 Thermal Throttling when connected to an external Monitor (4K BenQ) via DP to USB Type-C

So partially resolved the problem i did two things:

1. bought usb-c hdmi cable (previously i had belkin hdmi adapter),
2. opened a lower case and i noticed a lot of dust in fans and in vents so i cleaned it

Now since couple hours, i don't have thermal throttling and fans running around 3700rpms with ext mon so is OK. 

The funny thing is i have a couple MBP's, oldest what i have is 6 years MBP13' and I never clean up fans... probably MBP16 sucks more dust and needs to be clean up sometimes...

This computer was built with a ninth generation 14nm Intel processor. The only way to meet the target performance was to make it a six or eight core processor. This processor generates an enormous burst of heat when it does Turbo Boost, and there is only one cooling rail shared by both the CPU and GPU. So getting Either side too hot ramps up the fans.

This processor was supposed to be an eleventh-generation 7nm processor, but intel is three years late, and is only starting to ship its tenth generation 10nm processors now.

Apple DID redesign the cooling system for this specific Mac. New, high-efficiency fans are used. But for some uses, that is still not enough.

Some of the best advice is to install Turbo Boost Switcher and turn off CPU Turbo Boost. This reduces the huge sudden overheating brought on by Turbo Boost, that simply does not translate into real-world performance gains.

Changing away from HDMI to DisplayPort family (or to ThunderBolt-display or USB-C display) will reduce the Voltages and slightly reduce the heat generated. It is a good thing to do, but it may not be enough to solve this issue by itself.

How to fix your 16-in MacBook Pro (Don’t return it!)

https://www.youtube.com/watch?v=EkmdHVfk4XE

kernel_task taking over is running a "cooling loop", running low stress instructions while blocking other processes from heating up the processor even more when internal temperatures are too high.

kernel_task running so high is not the problem -- the excessive heating is the problem. The biggest tool you have to turn down the heat is to disable Turbo Boost.

If you are using HDMI interface to your external displays, it uses higher voltages than DisplayPort family or DisplayPort over ThunderBolt or USB-C. Switching to DisplayPort family when available can make a modest difference.

I have exact same issue.

16" 2019 with AMD Radeon Pro 5300M 4GB, Connecting external monitor via Thunderbolt + Video call with any software (Teams, Starleaf, Skype4Business),kernel_task goes to 1000%. It was never an issue before upgrade to MacOS 11.4

Resettig of SMC and NVRAM doesn't help

I’ll toss out a simple “mechanical” consideration:

Ensure that the laptop is placed on a surface so as to not restrict the cooling air “side” slots (underneath both sides) …

… or the “rear” slots. (under the display hinge)

Just a thought.

[My own 2017 15” MBP feels like a toaster when driving it’s two, 5k external displays]

Hi johnenova,

We see you're having some performance issues with your Mac when your monitor is connected to it. To clarify, is your monitor connected directly to the Mac or via an adapter? We'd recommend reseting your SMC and NVRAM to see if that clears up your issue. We've included articles on how to do both below:

How to reset the SMC of your Mac

Reset NVRAM or PRAM on your Mac

Take care.

I have exactly the same issue after upgrade to 11.4, kernel_task goes to 900% on basics tasks when I have ext. monitor connected. This is serious fck because Mac is totally useless. When is it happening CPU is cut to 800mhz...

It is placed on the surface, desk with very good airflow...

Mac working ok when i have closed the lid and also when i have not connected ext monitor. The problem will start when i have connected the external monitor and open the lid

Before 11.4 it was very noisy with ext monitor but without significant throttling. Now is noise and kernel_task coming to 900% so mac is useless.

Maybe they doing specially to force some users to upgrade to m1 ;]

That’s great news, thanks for the update. 👍

Re “dust” … it demonstrates once again that: “One can’t solve all mechanical problems w/ controls”

Might I ask for the make/model of your new USB-C -to- HDMI cable?

(I might invest in one for my own field kit)

Sure I bought this one on amazon

https://www.amazon.de/dp/B07925J6GY/ref=pe_25095781_587319921_TE_SCE_dp_1

Thanks!