I use a MDD G4 867mhz as one of my regular "use" machines, so I have some advice.

First is downgrade to 10.4 - Tiger.  The reason -- to get the temp down you need to use CHUD 3.5.2.  This allows you (automatically) to enable "nap" mode which steps down the processor's power in steps depending upon how busy the processor is (just like laptops do).  There is a startup script to automatically enable nap mode - but it doesn't work properly under 10.5.  You can manually turn on nap mode with 10.5 but it gets very annoying very quickly.

Nap mode makes a "HUGE" difference.  My MDD isn't as fast as yours but still I was experiencing temps that were on the verge of a meltdown before I did this.  Another option is to add some papst fans in there to help with the circulation a bit. 

So:

1. Install 10.4.11

2. Install CHUD 3.5.2

3. Install the CHUD nap mode script into the hdd, set it to a startup item in the control panel under your user account.

4. reboot

5. Enjoy a lower temp, reasonably usable MDD G4

Send me a PM if you need any of the files.

mitchW said:

I use a Hardware Monitor application. The room is 22 deg C. Well, the sensor does seem to work okay, since when it is first started, the temperature is nice and low at 32 degrees C, then it starts to rise. Also, at first, when it was crashing, the temperatures were about 65 degrees. I correctly oriented the fan. PSU fans were replaced with quieter ones. Original ones were 37 CFM, these are 30 CFM.

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