MacBook Pro (16-inch, 2019) hot & noisy fan when second monitor plugged via USB-C

Question

I have a problem in over heating and noisy fan when I have the second monitor plugged via USB-C (I have tried different types of external monitor, and the problem does happen with every monitor).

I can measure the Fan speed via istats:

$ istats
--- CPU Stats ---
CPU temp:               58.38°C     ▁▂▃▅▆▇

--- Fan Stats ---
Total fans in system:   2
Fan 0 speed:            5389 RPM    ▁▂▃▅▆▇
Fan 1 speed:            4927 RPM    ▁▂▃▅▆▇

I'm quite sure that the problem is caused by the second graphics card (AMD Radeon Pro 5300M 4 GB).

I have two questions:

1. How can I measure the graphics card temperature to be sure that the problem is caused by the graphic card?
2. How can I resolve the problem?

Answer 1

You can use macs fan control to get a menu bar indicator of any temp sensor you like as well as the fan’s RPM. This utility can also be used to set a more aggressive fan curve based on your GPU’s temp, but it’s a good rule to never set it to less or to a low constant value. This can cause random thermal shutdowns and sometimes damage.

I am not sure about resolving the problem. Unfortunately, the macs fan curve is already pretty silent, so if it’s ramping up, you have a lot of heat. You may need to use a utility like RDM to change your monitor's resolution to non-retina (change the resolution from the lightning bolt to the same resolution with no lightning bolt, disabling retina while keeping the scaling the same). This will reduce the load of your GPU by a considerable amount (for example, 1080p uses only 1/4 of the power of 4k). This comes with the drawback of blurrier text, so if you try this route and like it, make sure to enable sub pixel antialiasing (via terminal) for crisper text.

Answer 2

I had the same problem. I cleaned all the cable connectors and thunderbolt ports and experimented with using different ports and it solved the problem completely. Others mention using a port on the right for charging and/or checking if one of the ports feels hotter than the others to determine where the problematic one is. Not sure but I settled for charging cable on the right as well.