I installed Lubuntu 18.04 LTS after it was released. Unfortunately, the CPU temperatures never were below 70 degrees Celsius. I could toast bread on the laptop. To reduce overheating:
1. Go to BIOS and change Graphics from Optimus to UMA.
2. In Lubuntu, make sure NVIDIA is disabled.
The problem with Ubuntu 18.04 LTS is that all third party drivers must be signed officially by their coders. Unfortunately, that is tedious and cumbersome. Better to disable NVIDIA graphics altogether if you do not need it.