MacBook Pro high CPU with external monitors

Solution 1:

Folks this is an image of my fans before I had them cleaned.

I faced the very same issue that you guys are facing and based on input from another forum decided to get my 2016 MPB fans cleaned out. This made an immediate impact where when I connected my external display to the MBP.pre-cleaning, it would overheat causing the fans to spin at 6000 rpm or thereabout and the kernel_task would eat up 500%-900% of the CPU rending the system unusable. This simple cleanup of the fans has allowed me to connect the monitor with no kernel panic anymore and even though the fans run around 5000 rpm now the CPU and GPU are running around 10 degrees cooler now.

Solution 2:

I've been using a LG 27UL750 since almost a year with my MBP 16 i9 2020 connected via a HDMI cable using the Apple AV adapter.

I noticed that the fans on the laptop used to ramp up after 15 minutes of use and continued like that for the rest of my work day.

CPU usage was then in the mid 30s and performance was not impacted.

Yesterday I added a second 4K monitor that connects using Thunderbolt 3. When both monitors are connected and the laptop lid is closed I noticed that CPU was running at 70% with temps for both CPU and GPU at 65 degrees C, performance was really bad too.

I replaced the cable of my older monitor with a new USB C to DP 1.4 cable and the temps and CPU usage has been absolutely fine. I can't really hear the fans ramping up any more unless I'm compiling code or watching a 4K movie.

Using a crappy HDMI cable was the root cause, the cables that come with your monitor are a definite NO NO. Investing in a good quality cable is important for your Macbook to work well.

Solution 3:

Did you ever think about forcing to set a higher speed for the fan? Maybe smcFanControl or Macs Fan Control it would help.