Mac OS X 10.3.8 Special Report: Increased G5 fan activity

CNET staff

Sept. 2, 2009 10:56 a.m. PT

4 min read

For some users, cooling fans are significantly more active on PowerMac G5s after Mac OS X 10.3.8 is installed.

It now appears that this may be an intentional modification intended to reduce the incidence of "thermal runaway" events (covered in previous MacFixIt articles 1 and 2) which can cause kernel panics and problems with sleep.

MacFixIt reader Ed Rashed writes:

"For me, the increased fan activity since downloading the 10.3.8 update seems to have resolved a much more serious issue: I am on a dual 2 GHz G5, 1.5 GB RAM, and for some time I have had an issue with the system just spontaneously dropping into sleep mode. The system.log showed a 'Thermal runaway' causing the system to put itself to sleep, although the tasks that the processor was being asked to perform should not have caused this by any stretch of the imagination - it happened when: opening a link or even just a menu in Firefox, and sometimes for no apparent reason at all. Once the computer went right back to sleep as I was trying to log in from sleep mode.

"I read reports elsewhere that others with similar problems had had their motherboards replaced with mixed results. Others reported that changing or eliminating external power strips helped, and actually, my situation improved somewhat when I plugged the computer directly into the wall. But still, off she went to sleep every so often. Now with this update my fans do engage more often, but the narcolepsy seems to be cured. Seems that one of the undocumented fixes in this update is that Apple has reset the software thresholds to engage the fans sooner and thus prevent these "thermal runaway" issues. Maybe those initial reports of how quiet this computer was supposed to be were based on a higher threshold setting that then allowed the thermal problem to surface. Anyway, I am glad to trade the fan revving for a computer that stays awake"

The increased fan activity, and consequential decrease in processor temperature, has also apparently resolved some other stability issues

MacFixIt reader James Taylor writes:

"I recently installed the 10.3.8 update on my Rev A. dual 2.0 G5, and I noticed the fans will rev a little bit when opening apps and the like. [...] When browsing a particularly large series of files (like my music directory) in detail mode, sometimes Finder would pause, hit 100% usage on the CPU, and sometimes crash (it would recover a good 2 out of 3 times, if I remember correctly.) The 10.3.8 Finder does not exhibit this behavior, even with huge directories of thumbnails.

"I think the fan differences might be an effort by Apple to keep the chips a little cooler. X-Resource Graph shows a difference of a few degrees since installing the update, possibly as a result of increased fan usage. It's not a huge drop in temperature, and praise goes to the Apple engineers for designing such a wonderful case."

The only effective workaround we've seen is to change the Processor Performance setting (in the Options tab of Energy Saver preferences) from Automatic to Highest -- a number of readers have reported that this "fixes" the increased fan activity. (It's odd that this results in reduced fan activity, considering that the Highest setting should make the processors run hotter.) However, note that by doing this you're circumventing your Power Mac's built-in processor regulation system -- instead of running at full speed only when necessary, your G5 processors will be running at full speed all the time. We wouldn't consider this a prudent long-term workaround.

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