So yesterday my 9800gt started acting up. On GPUZ it said the fan was at 5% with an rpm of 9500+ which "9000+" is the equivalent of 90%. I tried reseting it in rivatuner but to no avail. So now I'm stuck with GPUZ saying my card is at 61c (when it's probably 40F in my room).
Things I have tried:
1. Reistall GPUZ
2. Reinstall RivaTuner
3. Installed new nvidia drivers (note: I saw the problem BEFORE I installed the new drivers)
Q6600 (not OC'd)
4Gb ddr2 800
Vista home 64bit
If your card or cooler is defective then you can RMA it.
Maybe there is not enough thermal grease under the cooler's heat sink.
Please note that removing the cooler could void the warranty even if it is a good practice. I've seen people removing it and adding more thermal grease and the problem is solved as well as the temperature reading is correct. However, check to see if your brand's warranty does cover up the removal of cooler/re-modification of the video card's cooler and overclocking. For example, EVGA does allow you to overclock and remove the cooler without affecting/voiding the EVGA's warranty.
I think that your case is similar to those who have problem with CPU's fan and temperature reading. It was a technical problem like not having enough thermal grease and the heat sink isn't placed properly...