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Thread Starter 
This is a BETA fix so beware if you want to try it:

DON'T TRY THIS IF YOU ARE A BEGINNER
USE AT YOUR OWN RISK


My iMac G5, 20" 2GHz, was getting pretty hot, doing pretty normal stuff like web browsing, some web development, and Photoshop work. I noticed it when I started getting intermittent shutdowns and KPs shortly after the fans would go full speed. So I started monitoring my temperatures with a utility like "Temperature Monitor" or "iStat". My temps were pretty high I thought; in the 170-178 degree range. So I embarked on finding a solution. I was hitting a bunch of dead-ends. I found many articles on XLR8yourmac and other sites with other iMac owners with the same issues. Some have even had multiple motherboard replacements. But no solutions or if there were solutions, they involved strapping external fans to the back of the iMac with an external power supply to pull hot air out of the computer.

And then I stumbled on an old OS X fix for the MDD G4 tower that involved modifying a kernel extension to lower the temperature threshold of when certain fan speeds come on.

The file is an Info.plist in the /System/Library/Extensions/AppleFan.kext file (Show Package Contents). I made a copy of the original file and gave it the same permissions of the original. That way, if something bad happened, I could single user mode into the system, delete the old info.plist file and rename the backup. You're basically looking for this text:


Code:

<key>fan-hysteresis-temp</key>
<integer>14080</integer>
<key>fan-polling-period</key>
<integer>8</integer>
<key>fan-slowdown-delay</key>
<integer>48</integer>
<key>fan-speed-table</key>
<array>

<integer>

14592</integer>
<integer>14922</integer>
<integer>15059</integer>
<integer>15164</integer>
<integer>15252</integer>
<integer>15331</integer>
<integer>15401</integer>
<integer>15466</integer>
<integer>15526</integer>
<integer>15583</integer>
<integer>15637</integer>
<integer>15688</integer>
<integer>15736</integer>
<integer>15783</integer>
<integer>15828</integer>
<integer>15872</integer>
</array>



The first number under "fan-hysteresis-temp" and the 16 numbers in the array are the temperature thresholds in C multiplied by 256. What I wanted to do was lower the temp that the fans kicked in at by 5 degrees. You may want to start with a lower number like 3 and adjust from there. So 5 x 256 is 1,536, so I subtracted that number from all 17 numbers that are highlighted blue above. I restarted, unplugged the power to reset the SMU, plugged it back in and powered it back on. 2 hours of use later, the temps are now range between 130 and 140 doing normal stuff, and Photoshop can hit it to 155 but I think it's acceptable. The fan noise is definitely there but to me it's barely noticeable.

I would only try it as a last resort, YMMV. One thing that helped a little was opening the iMac and cleaning out the dust.