Originally Posted by
r4st4m4n
After opening your bios in Nibitor, go to the tab "temperatures", then click on Fanspeed IC.
There, if you select "automatic Speed, you can play with Tmin, TRange slope and min duty cycle to have the fan speed increasing according to the temperature of the core. The mechanism / thresholds are well described in nibitor itself.
IIRC for my 8800GT, I have set Tmin to 60*C, TRange slope to 20*C and min duty cycle to 30%.
As result the fan speed will slowly increase when the core reaches about 64-65 degrees. The temperatures will stabilize at about 75 - 80*C depending of the load, with the fan spinning at about 60-65% at this temps, although in nibitor it says that at 80*C the fan should spin at 100%.