MBP fans problem - help

For some strange reason, it doesn't seem like my fans are increasing above 2000rpm. I've been doing a lot of work (encoding music, and running a lot of programs in VMware fusion) and i noticed it was really heating up, so I checked iStat pro and it said my CPU diode was approaching 80C (one of the highest temps I've seen), but the fan speed is still at 2000rpm! I had to download smcFanControl and turn it up to 5000rpm for a few minutes. after I quit smcFancontrol my MBP started heating up again and the fans wouldn't increase! what is going on? my fans always used to spin up... even sometimes when it wasn't very hot... (maybe that was the beginnings of a problem?)

is there some system prefs setting for this???

 

update:

the fans went up to 2200rpm for a minute, but now they are back to 2000 with the the temp at 80C.