I was using iMac Fan Control by Derman Enterprises which is really good, but the preferences panel is not 64bit (a bit annoying) and the HD temperature sensor doesn't works for the new models of iMacs. So, I did some changes on this great application. I am not sure if this sensor will work on the newest models of iMac (or if you have replaced the factory hard drive), but I hope so (if it did not work you will have no trouble at all, only a fixed speed for the HD fan). First, you need to download and install the iMac Fan Control (if you don't use it yet). After installing it, download the modified files (include sources) on this post and them double click extracted preference panel, and for the Daemon you do the following, in the terminal: Code: sudo killall FanControlDaemon sudo mv [U]/FanControlDaemon[/U] /Library/StartupItems/FanControlDaemon/FanControlDaemon sudo chmod 0755 /Library/StartupItems/FanControlDaemon/FanControlDaemon sudo chown root:wheel /Library/StartupItems/FanControlDaemon/FanControlDaemon For the second command, you should put the extracted FanControlDaemon in your "/" dir ("Macintosh HD" root, or edit the command with the file path). Just reboot and you are done with it, now you can just configure in the Preferences or leave it alone. I leave my iMac powered on 24/7 and it's always cool as if I just started using it. The best settings (at least for hot country) is: Lower Temp Threshold: 46C Upper Temp Threshold: 85C Slowest CPU Fan Speed: 1200 Slowest HD Fan Speed: 1600 Slowest DVD Fan Speed: 1600 This will keep your iMac aways cool, even in 100% full load. The HD + DVD (mostly) fans will keep your GPU cool too. If you try please leave a comment. (Specially about the settings/results and if the HD temperature is working fine, and what is your model). Soon as I get some free time I will change the Daemon to work on 64bit too.