To better explain what philibar said:
open RivaTuner > on the 2nd section (under Driver Settings), there will be a little arrow by the word Customize. Click it and a hover menu will come up > click the first picture that looks like a graphics card (hover over it and it says 'System Settings') > Click the Fan tab > on the pull down menu, select Direct Control > adjust the 3rd slider > check the box that says "apply at startup" and click Save > click OK.
To check temps with Rivatuner:
On the main window, under Target Adapter > click the arrow next to the word Customize > click the picture that looks like a microchip with a magnifying glass on it (hover over it and it says Hardware Monitoring) > brings up a window with graphs; look at the Core Temperature one.
Edit: to setup an auto-fan profile: RivaTuner 2.0 fan speed & Overclock Guide