PowerMac G5 CPU Fan Cycle. Annoying! What To Do?

Discussion in 'PowerPC Macs' started by tjwaido, Nov 9, 2008.

  1. tjwaido macrumors member

    Aug 24, 2008
    The wild west.
    I recently noticed an annoying fan cycle on my PowerMac G5 Dual 2.7 Intake and Exhaust Fans. The fans will go on a power cycle for a few seconds and the power down for a few seconds, and then the process continues over and over again. iStat Pro (Dashboard Widget) shows the fans will rev-up to 3000 RPMs and then cut out before the process happens again. This occurs all the time even when no programs are open. The fans will kick-in when performing intensive CPU operations using Aperture or Final Cut Pro and perform like normal. I have gone to System Preferences and set my Processor Performance to Reduced, but the fan cycle continues, just at lower fans speeds. Although, the fan noise is less annoying. I have checked my heat sink for dust and other obstructions, but it looks to have a clear air way.

    I am not sure what to do? If there is anyone else who is experiencing this problem or has resolved this issue, I would like to know. Thank you for any help you can give.

    PowerMac G5 Dual 2.7Ghz
    Mac OS X 10.5.5
  2. product26 macrumors 6502a


    May 30, 2005
    You may be able to download a program that allows you to bump up the minimum fan speed a little. This should prevent the processors from heating up as much, reducing the need for shoe bursts of cooling.
  3. sickmacdoc macrumors 68020


    Jun 14, 2008
    New Hampshire
    I understand that it is not really helpful to tell you that my backup machine is identical- a DP 2.7 G5 and it has never exhibited this behavior- but it got me thinking that I read that one of the symptoms of the early stages of the liquid cooling system leakage problems included unusual fan behavior. I could well be wrong on that (and actually hope I am).

    I don't say that to concern you, but as a thought in searching for an answer. If you are not familar with the liquid cooling leakage problems, there is a whole section at xlr8yourmac.com concerning that that you probably should review if for no other reason than to be aware of things to watch out for regarding it since our systems are affected by it. You can find the section at LCS leakage.

    Good luck- and if I stumble across anything more clear about the kind of "cycling" it seems to be doing I will come back and pass it along.
  4. IroquoisPliskin macrumors regular

    Oct 11, 2008
    There is no such thing for the PowerPC models.

    Thats what came to mind for me. Open the case and look for green liquid.

    What did iStat Pro show for CPU temperatures?
  5. TheReef macrumors 68000


    Sep 30, 2007
    NSW, Australia.
    I experience this behavior on my 12" Powerbook when setting the threshold limit very close to the current temperature.

    I'd say the heat is just peaking over the threshold temperature, when the fans kick on the temperature is reduced…then the temp goes back up etc.

    If you can't adjust the fans, the only option I guess would be to move it to a cooler place or some how get some cooler air near the intake grill, to move your running temperature away from the threshold value.
  6. tjwaido thread starter macrumors member

    Aug 24, 2008
    The wild west.
    Oddly enough, I haven't had any major issues today. The temp in Colorado was freezing today and my condo temp was cooler as well. Cooler air might just be the solution to this fan cycle. Currently, the temps are CPU A: 58-60°C, CPU B:60-63°C, with fans speeds between 300 and 1300. I don't know my room temp or CPU temps when it was doing it's fan cycle, but I will try to keep that in mind when it occurs again. I checked for coolant leakage, but I didn't notice any liquid.

    All the comments have been helpful. I am sure the fan cycle will occur again, I have noticed it for about a month at different times. It is definitely an irregular thing and when it is happening, it is irritating.
  7. Earl Urly macrumors regular

    Jul 11, 2004
    If you take your G5 to the Apple Store you can ask for something called a thermal calibration. Sometimes the thermal calibration sensors need to be calibrated after years of use, the Geniuses have access to a special utility only for g5 macs that can do this. Try this if possible
  8. leekohler macrumors G5


    Dec 22, 2004
    Chicago, Illinois
    Do as others have suggested here and take it to the store. My G5 never has erratic fan issues like that. They're always at a constant speed.
  9. California macrumors 68040


    Aug 21, 2004
    My single 1.8 did this until I set something to HIGHEST. I think it was processor speed or something. Very annoying fan noise like up and down on a roller coaster until I reset this.

    Make sure no liquid and that the inside is dust free as possible, too.
  10. scottlinux macrumors 6502a


    Sep 21, 2005
    Yes there are apple service discs that can calibrate the fans of G5 machines. Apple does not release these for the public, unfortunately.

    Any apple certified desktop tech has access to obtain these discs and can help do the job.

    Blow out the dust also, as someone mentioned above. Especially dust from the power supply fans at the bottom.
  11. OrangeSVTguy macrumors 601


    Sep 16, 2007
    Northeastern Ohio
    Yep. If you go to System Preferences and then to the Energy Saver icon, Click the Options tab and select the Processor Performance to Highest. I don't think I ever heard my fans rev above 1000rpm yet or seen them using iStat widget. Even with CPU(s) at 99-100% for 3 days straight.

    How dirty is your system? Have you ever cleaned the fans inside? They can get dirty and dusty fairly quick and often. Especially the power supply unit.
  12. tjwaido thread starter macrumors member

    Aug 24, 2008
    The wild west.
    I plan on cleaning the inside soon. There is dust but it isn't caked on. A few years back my system was over heating and shutting off automatically. My entire heat sink was clogged with dust. I never had this problem again, because I do check the air flow relatively often now. I haven't had the system do it's fan cycle for a few days now. Ever since I posted this forum I have kept my office cooler, which has seemed to help. I believe I lowered the temperature threshold as suggested, but I am waiting for it to do it's thing again.
  13. fhturner macrumors regular

    Nov 7, 2007
    Way late to the party here, but hey, you never know who might have email notifications turned on! :p

    tjwaido, did you have any further reoccurrence of this? SVT (and others), what OS version are you running? I have a Dual 2.5 that used to behave itself nicely under 10.4 Tiger, but when I upgraded to 10.5 Leopard, its fans started suffering from ADD or something. They rev up for maybe 2 seconds or less, then drop back down, then rev up again, in random patterns. Just the slightest bit of CPU activity triggers it, and I can't even imagine that the temperature even has time to change appreciably before the fans jump up, then back down.

    Anyway, HIGHLY annoying. Oh, this system has had thermal calibration (again, it behaved nicely under 10.4) and has been dusted out. Another G5/2.5 I used to have also behaved similarly, so we may just be SOL if we want to run Leopard on these guys...

  14. MrJolly macrumors member


    Aug 15, 2011
    I live next door, England
    Open System Preferences and then launch Energy Saver. Select the Option button at the top and set the Processor Performace to something other than Automatic.
  15. fhturner macrumors regular

    Nov 7, 2007
    Thanks for the suggestion, but if I've gone as far as thermal recalibration in Apple Service Diagnostic, you can bet I've played around w/ the Energy Saver settings, too. :D The Processor Performance setting doesn't have any effect for me.

    The other day I was observing the behavior w/ iStatPro, and noticed that it looks like the CPU temps are climbing from around 120-130F to 140-150F (so, each gaining about 20 degress), then the fans ramp up briefly, the temps drop back to the initial 120-130F range, and the fans quiet back down. Then the dance begins again. It isn't a regular cycle, tho...frequent, but not like a drum beat or anything. Then, of course, any significant CPU load beyond idle will yield a big jump in fan speed. I've even tried another run w/ the thermal calibration, but if you've already done it and the CPU/hardware arrangement hasn't changed, the calibration will not proceed.

    BTW, I have a new Back-UPS XS 1000, which has a handy readout that displays power draw. At idle, this Dual 2.5GHz G5 is drawing about 151W. When the fans ramp up, the draw jumps up into the 300W+ range. I do not think much of this extra usage is attributable to CPU, as the graphs over time do not rise very much.

    One thought I had that helped significantly on a Quad G5 not long ago was to remove the CPU cards from the heat sink and apply new thermal grease between the two. Anyone think this might improve things here? Probably wouldn't hurt...just a pain to get at!


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