Touch Bar iStats shows temperature of CPU/GPU/MEM or whatever you want sensor on your touch bar.
sudo gem install iStats(you can use macOS embedded ruby,
Gauges will turn red when a safe temperature is exceeded:
You can change probing interval in BetterTouchTool on widget's Advanced Configuration dialog.
btt-json-presets folder contains presets in older format.
Touch Bar iStats is published under the MIT License.