engine fan and temp gauge dosen't work

Hi I own a 95 buick century with a 3.1 liter engine. I have a couple problems that I'm looking to solve. First is that the temp gauge goes straight to hot and stays there. I tried changing out the coolant temp sensor (thing that looks like a 3/4ths bolt with a cannon plug) and that didnt' fix it. Any suggestions? The other problem is that my engine cooling fan dosen't turn on. Right now it's wired to the interior fan switch, so now I have to keep the interior fan blowing, to keep the engine fan running. Is there anything I can try to get the fan working the way it's supposed to? Thanks