Nvidia Cards have their fan speeds at 40% for me it was a bt of a problem.

What i did to increase the speed of the fan(s):

I installed nvclock from package manager.

Then i went to my home folder and created an empty file. For me i name it nvidiafans

I added the follow:

#!/bin/bash
nvclock -f --fanspeed 70 (i wanted the speed to 70%)

save and close.

Then i right click on the file and go to permissions tab, tick on Allow executing file as a program

close.

Now we need control center --> startup applications --> startup programs

I clicked on add and for name you can put whatever you want.

On command i clicked browse and i click, open the file i created before in my home directory nvidiafans

After just click on add and make sure its ticked.

Close everything and re-boot

Enjoy.