I'm currently using Ubuntu 18.10 on a machine with Nvidia OPTIMUS (GeForce 650M on Samsung NP550P5C-S01IN). Currently for Nvidia, I'm using nvidia-driver-390, though current selected GPU is Intel.
My idle CPU temperate resides in the range of 68C to 75C (154F to 167F) which is too hot. The weird thing is that the fan runs at really low speed. I know the fan can run faster because during GRUB screen, before selecting the OS, the fan spins much much faster (can even hear it).
Yesterday, I even cleaned up the fans and replaced thermal compound, which only helped with lowering like 2-3C.
The fan does not have speed control but in Windows 7, I did used to have the option to run the fan 'silently' (i.e, slower).
Hope I can get some help with this.