(If you don't know the answer to this, would you mind forwarding the link on to someone who might? I am kinda worried about my G5).
The last few months I've noticed that the fan in my Mac G5 (the last generation before the new ones with the Intel chips) has been running more and more often (I think) and at higher and higher speeds. I thought maybe it was dirty and opened it up to clean it, but the area with the fan is behind so many bolts I didn't know how to get to it.
The fan has been running all day today without interruption, and it's a very warm day.
I assume the fan runs to keep the CPU temp down. So I've been monitoring the temp of my CPU. What's too hot? Here's a snapshot of just now.