My own symptoms was reduced by properly cleaning my laptop fans, but the cpu still seems to be running about 5 degrees C higher on average compared to LM18.
On LM19 i noticed an additional "ghost" VGA display in the Display Settings, as seen in this picture (I only have one additional display attached to the laptop):
I thought I had seen the issue before, and while searching for a solution again today, I stumbled onto this bug report. Notice comment #70:
I guess this old kernel bug found it's way back in Ubuntu 18.04 (the new LM base), and it would explain why at least for me there does not seem to be a difference in temperature when I switch between Nvidia and on-board gpu, which there definitely was before LM19.Affects me too on an Asus N43SL with nvidia GeForce GT540M.
The extra screen is detected both by nouveau and the nvidia proprietary driver.
On Ubuntu 18.04 which relies on nouveau to turn off the dGPU, this prevents the nvidia card from shutting down, which causes useless battery drain and heating.
There is no fix for the issue yet, but I guess there will be, and I just thought I would mention it here, in case anyone where experiencing similar heating issues.