OK, I've officially given up on fixing this fan/heat issue on my PB12. I want to express again my appreciation for all the ideas and support here, and to summarize for anyone else facing this problem the main things I've learned.
1. There really is something inherent in Tiger that makes Macs run hotter. My current opinion is that it's related to the fact that many process threads formerly handled by the CPU have been shifted to the Graphics processor. The result of this is that Tiger runs blazingly faster on many tasks, because the Graphics unit is vastly more efficient at those tasks. The downside is that at least some Macs (my powerbook, for example) aren't designed to handle the extra heat produced, without the fan coming on.
2. There's currently nothing that can be done about the shift of graphics routines to the Graphics processor. Maybe Apple will offer something to throttle down its speed as is possible now with the CPU in System Prefs/Energy Saver. Maybe someone will find a library that can be swapped in from an earlier version of OS X, as is now possible for fan control by swapping in a file from 10.2.8 as described elsewhere.
3. Just turning off the fan will solve noise issues, but won't help with the extra heat. Therefore, someone like me who uses a PowerBook on their laps will trade a noise issue for a heat issue and possibly also a durability issue due to the higher operating temperature. Turning down the CPU speed in Energy Saver will help if your CPU load is high, but often CPU load's not the cause and it also means a slower Mac.
4. Some Macs, including PowerBooks, seem to have a Graphics unit that's designed to handle heat better and/or generate less of it when running the fabulously superior graphics routines in Tiger. I haven't tried to track which models those are, but they seem to be some of the newer ones than mine.
5. If you are having heat or fan problems, the first thing to check is what processes are running and what your total CPU load is. As with all versions of OS X, if you have processes using up 100% of the CPU time for extended periods, you're going to have heat problems (and the fan will come on if your model has one). In the Applications/Utilities folder you'll probably find Activity Monitor, which you can use to find out what processes are running and how hard the CPU is working. Keep in mind that the load changes depending on what application is in the foreground, so you might position your open windows so that you can switch between apps and still see the Activity Monitor to note any changes in load conditions.
6. There are several common problems with relatively simple solutions that can completely eliminate heat and fan problems on many models. These include: Virex (find and remove all traces, and make sure there's nothing like that in your list of running processes); Dashboard Widgets (several of these have been found to cause heat/fan issues, so try turning them all off); Norton and several other utility programs.
The most common heat cause of all after newly installing Tiger is Spotlight, which goes nuts for up to a day or more indexing all your files. If your investigation with Activity Monitor reveals high CPU load, you can: a. find out what the names of the Spotlight processes are and see if those are the CPU hogs; b. temporarily turn off Spotlight indexing by opening System Prefs/Spotlight, clicking on the + sign in the Privacy tab and adding your hard disk and any attached drives; c. leave your Mac running with screen turned down or off and sleep mode turned off for a day or two.
7. If like me none of the above issues applies, your Activity Monitor will show about 3% or less in CPU load yet after the Mac's running for a while it starts getting hot and if you're doing certain things the fan will come on and then usually stay on. For me a great way to get the fan going is to log in via dialup (haven't tried WiFi yet to see if that does it too). My belief is that the modem puts out just enough extra heat to get the fan going. Some applications contribute too, like Eudora 5.2 which can spike up to 70% on CPU load when I'm composing an email. I've also found that launching FileMaker 3 or 4 in Classic will immediately peg the CPU load and get the fan going full blast. Classic in Jaguar 10.2.8 did the same thing for me, but in Tiger it also adds a cute little keyboard repeat stuttering problem. In case you're wondering about a clean install, I haven't tried it but have seen posts by several who have tried it without success. I did try booting from the DVD, and the fan came on pretty quickly.
8. One last hopeful note. Since installing Tiger using Upgrade from 10.2.8 last week and after Spotlight had done its thing, I've noticed a gradual continuing improvement in heat/fan issues (possibly improving with each subsequent Restart). The heat takes longer to build up, and the fan takes longer to come on. A few times it has even shut off again once it did start. There may be something automatically adjusting itself somewhere in the bowels of the Tiger that accounts for this, the hard disk is cooler due to defragmentation, or maybe the fan's just clearing out dust that had built up inside the case due to the fan not running before (though I've seen no signs of dust anywhere).
If anyone here has access to MacFixIt, I'd appreciate you posting something about heat/fan issues there, because I've seen no such mention. If I had, it would have been a great help in deciding whether to upgrade and in dealing with the issues I've been so distracted with for the past week. There are plenty of references elsewhere online, but of course I wasn't lucky enough to have seen them before buying Tiger.
I like Tiger, and still haven't decided whether to revert to Jag and wait for a solution. First because I doubt that a solution will come, and second because I like some of the new features including the speed increase.
Enjoy
About This Mac: 10.4.1, G4 867MHz, 640MB DDR SDRAM, 40GB.
Weiß gar nicht, was der G4 braucht.
