How to reduce the minimum fan speeds on iMac?

Discussion in 'iMac' started by had2B, Jul 26, 2009.

  1. had2B macrumors newbie

    Jul 26, 2009
    I have a new mid-2009 iMac 24 inch 2.66GHz. I work in a quiet environment and most of the time the computer is idling along. iStat returns the following fan speeds:
    CPU 1200
    HDD 1600
    ODD 800

    Even when I drive the iMac a bit harder - 100% CPU for an hour and a half - the temps only rise as follows:
    CPU 60 C
    Northbridge 68 C
    Power Supply 71 C

    and the fan speeds do not increase.

    I value silence, and it seems to be unnecessary for the fans to running at this speed when they are not needed most of the time - when the computer is not under any load. With the iMac everything is right in front of your face. I heard about iMac Fan Control and installed it, but there is no possibility to set lower-than-standard fan speeds, except for the HD which can be set to 1200 instead of 1600. However, the ODD minimum speed increases to 1000 from 800.

    If I don't find a fix for this I will be sending the iMac back to Apple, and will have to reluctantly step down to a new Mac mini. Can anybody help?
  2. DavidR91 macrumors member

    May 24, 2009
    Bourne, Lincs, UK
    I'm quite perplexed as to why you would want your fans to go lower than the absolute minimum values:

    First off, your temperatures, whilst OK (and not dangerous) are not cool enough to justify reducing the fans further.

    Secondly, at those speeds it should be barely audible anyway - unless you live in a sealed sound-proof container, I'm surprised the noise stands out particularly.

    Overall, I'd say keep it, but leave the fans alone - or consider finding out whether your fans are nosier than usual (possible they could be a bit 'clunky' and it's not the speeds that are the problem). You most likely can alter the speeds below those values (direct manipulation of values under the SMC / EFI) but it is dangerous (from a temperature point of view, and the likelihood of severely messing up other values in memory if done improperly)
  3. had2B thread starter macrumors newbie

    Jul 26, 2009
    When it has been idling for a few hours with a few apps open the temps are like this:

    CPU 37 C
    HDD 45 C
    ODD 37 C
    Northbridge 61 C

    This is the situation in which I would like to have the fans running slower, which should be okay as even when the temps rise under load to those mentioned in my post above, the SMC doesn't feel it's necessary to increase the fan speeds. That's my logic.
  4. paulbeattie87 macrumors regular

    Aug 17, 2008
    North East Scotland
    What David is trying to say that the temps you posted are getting a bit on the high side, even what you have posted above, the hard drive sitting at 45 is relatively high. You got to remember the MAX operating temperature for a hard drive will be 60c.

    As for what you said about a computer being under load not needing any cooling, thats the first time I've heard that. Just because your computer is idling, the hard disk is still spinning making heat, the CPU is still processing nothing still creating heat, your PSU is still converting power producing more heat and so on. Going by your token why do computers have cooling at all? After all most computers idle for over 95% of the time they are running.

    You mentioned the iMac sitting in front of you making noise, I have in front of me a brand new 2009 24" iMac 2.93Ghz and it's as close to silent as I can imagine. If I sat any closer than I am, the display would be so close I wouldn't be able to use it.

    I've just had to return my 2008 24" iMac 2.8GHz because it's fans sat at 1200 on the CPU and HDD, 800 on the Optical Drive. Eventually it cooked itself to a slow death, hard drive sat at 60c all the time, display was damaged by heat etc etc.

    What your asking for is an Intel Atom with a fanless cooling system.
  5. dubhe macrumors 65816


    May 1, 2007
    Norwich, UK
    My mac mini, which you thought about replacing the iMac with, still has a fan, and on mine it is currently running at 1900 rpm and I can hear it, just... Not sure you would find it silent :(
  6. had2B thread starter macrumors newbie

    Jul 26, 2009
    What I was trying to express was the fact that the standard Apple SMC doesn't see fit to increase the fan speeds at all when the temps rise from ambient to these:
    CPU 60 C
    Northbridge 68 C
    Power Supply 71 C

    therefore I conclude that it is not necessary for the fans to be running at the same speed when the computer is "cold", or gradually warming up. Maybe the fans could run at half their "normal" speed at startup and gradually increase from there.
  7. Hellhammer Moderator


    Staff Member

    Dec 10, 2008
    CPU gets hot when it's under load, no matter what. Northbridge is part of CPU and it likes to run hot. PSU is hot of course because all electricity runs through it. I have all fans running ~2 times faster than default is and it's quiet IMO
  8. RValverde86 macrumors newbie

    Jul 26, 2009
    Just let this guy get the mac mini. It's obvious he's not willing to accept the fact that his iMac will burn if he changes the settings. He got all the info so now it's up to him.
  9. Shake 'n' Bake macrumors 68020

    Shake 'n' Bake

    Mar 2, 2009
    I'll throw in four things.

    1. There is a file (plist, I think) somewhere that is the master for the temps and you can edit it, increasing or decreasing the acceptable temperatures.

    2. You must have sensitive ears. All the iMacs I've used at the Apple Store and at my neighbors house have been silent, with the fan running.

    3. I keep my Mac mini's fan at 3000 RPM all day, because if I don't, the system doesn't react and the temps get to nearly 200 F (do the conversion yourself). I can't hear it with music playing and it is barley audible without music.

    4. If you want silence, get a G4 Cube or iMac G3 and throw a SSD in. Both are convection cooled, so it will be the quietest computer on your block.
  10. J&JPolangin macrumors 68030

    Jul 5, 2008
    Thule GL @ the TOW
  11. paulbeattie87 macrumors regular

    Aug 17, 2008
    North East Scotland
    I agree, my iMac usually hovers around the 4xC mark for most components, the PSU gets up to the low 60's. That said having already had one iMac cook itself I know how important cooling is for it.

    On my 2008 iMac, it's fans never increased, at late June the temps on the HDD were heading towards 70, PSU was heading towards 90, GPU was going a similar way! That's some cooking going on inside, despite all this, it sat with the fans running at the same speed as when the components were at 30c.

    Now I have a new iMac and want to keep it :p, I don't want to go running SMC Fan Control or iMac fan control because I've read that on newer iMac's even with a PRAM and SMC reset they are still in effect. I'd rather just take it and say well if it cooks at standard Apple will replace it like they just have!!

    My current temps:

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