Macbook pro 13" - 2017 - heating issues when connected to external monitor
With reference to Apple discussion:


The USB-C - HDMI converter I've been using was getting very hot. The heat was also transfering through the USB cable to the MacBook's body.
In addition to above, the Intel GPU is doing more work, so it is obviously getting warmer/hotter (you can see on the screenshot above, it is at 68 C).
In addition to that, the system controlled fan speed is too low (~1700 RPM) to allow for cooling when the skin temperature is rising over 40C.


I noticed that I can tolerate ~40C just fine, but 42C is not good for prolonged (more than 30 min) use. It gets annoying fast over 41C.

I replaced the mentioned USB-C to HDMI converter with a HooToo converter and that one is not getting as warm as the previous one. Also, the USB-C connector has much lower temperature than the previous one (so I guess heat transfer is not that much).

This didn't quite solve the heating issue, though.

I used iStat Menus to change the speed of the fan, so it is cooling more. With the fan speed set at ~5000 RPM, the skin temperature is around 39-40C with light use of computer (MS Word, browser -- 90% idle). I was even able to charge the computer, have it connected to the external display and use it with skin temp under 40C with the fan at its maximum speed. 

IMHO, the cooling system of the MacBook Pro is not suited for "Pro" use --
 at least not in a comfortable way. I believe this could easily be adjusted with an OS/firmware upgrade, so that he OS would turn the fan speed up when reaching skin temperature of 40C. 

I will also give MacFanControl a try, to see if can automatically adjust the fan speed .