When should the fans kick in?

Discussion in 'MacBook Pro' started by grooveattack, Dec 27, 2012.

  1. grooveattack macrumors 6502a

    Jan 9, 2008
    Hey Guys! Merry Christmas!

    I was wondering if anyone knows the temps that the fans on the rMBP are set to kick in at.

    My laptop seems to just randomly spin up even when im not doing anything.

    I've attached the temps and rpm below. I had just sat down and started the machine up and had safari open. The room was quite chilly and the computer was cold yet the fans span up to nearly 6000rpm for about 30 seconds.

    Thanks guys, take it easy.

    Attached Files:

  2. Barna Biro macrumors 6502a

    Barna Biro

    Sep 25, 2011
    Zug, Switzerland
    Although you might not be touching the notebook at the time it starts to spin up, you might still have software installed that forces it. The fans kick in based on some quite complex algorithms... the best way to put it: "they kick in when the machine 'thinks' they should". If they kick in under no load and low temps, then it might be caused by some other stuff that you have installed that is forcing the fans or just messing things up.

    PS: Does this happen often? Although it might seem "random" to you, I wouldn't just call it that yet. Try thinking about the kind of tools you were using before / at that time and see if you can come up with a pattern that might reproduce the effect.
  3. makaveli559m macrumors 6502

    Apr 30, 2012
    Mountain Lion has always been crappy with me on that with Lion I never had an issue with the fans kicking in. What ever Apple did instead of fixing it, its really ill.
  4. Dyno-Mike macrumors regular

    Aug 19, 2012
    United Kingdom
  5. tivoboy macrumors 68040

    May 15, 2005

    So, I've had my rMBP running up to 185 degress before, and the fans are still showing 2157 left and 2003 right (sometimes, they are a tad lower)

    I don't run smc fan control at all on this machine, or any other fan controllers.

    I'm concerned that having put one on for a couple trial runs, locked them in at 2K? Is that possible?

    What is the best way to TEST if the fans will ramp as necessary?
  6. Barna Biro macrumors 6502a

    Barna Biro

    Sep 25, 2011
    Zug, Switzerland
    185 degrees fahrenheit I'm guessing... which is roughly 85 degrees celsius. I doubt your machine was running a long period of time on that temp without fans ever kicking in. Again, since there is a quite complex algorithm that is responsible for determining when to speed up fans ( and it is dependent on quite a few factors ), it can happen that the fans don't kick in instantaneously when you reach a certain limit. They might kick in a few seconds / tens of seconds / few minutes later...

    Just to make sure your fans are properly working, you could actually download scm and force max rpm for a while. If that works, put it back to default and just continue with your normal tasks. Fans will kick in when they really need to.
  7. tivoboy macrumors 68040

    May 15, 2005
  8. switon, Dec 27, 2012
    Last edited: Dec 27, 2012

    switon macrumors 6502a

    Sep 10, 2012
    RE: apparently random fan "kick-ins"...

    Hi all,

    The fans's speeds are controlled by an algorithm that depends upon the internal temperatures of the various sensors within the rMBP. I've never been able to ascertain precisely the algorithm, but it is certainly true that whenever the CPU temperatures (and it depends on which ones) go above 90C (=194F) then Apple's fan control algorithm will increase the speed of the fans.

    You have to be cautious when reading internal temperature with the various temperature monitor tools, as different ones will report different temperatures. How is this possible, you might ask? Well, there are actually a number of temperature sensors, and since the apps typically only report one number, they are either just choosing a single sensor to report or are performing some sort of "averaging" of the many temperature sensors's values. If you wish to see really accurate values, I'd recommend Intel's own PCM tools for providing complete processor performance information. (Unfortunately, you have to compile these Intel PCM tools yourself on your computer and they run from the command line, although there might be a GUI interface to them that I don't know about.)

    About those apparently random fan "kick-ins" that last roughly 30 seconds....well, I suspect that they are caused by various system processes, and most likely the Spotlight indexing of your drives. If you attach an external hard drive to your computer that has not yet been Spotlight indexed, then Spotlight will attempt to index it. This takes CPU cycles and will load a CPU and heat it up, eventually causing the fans to spin up to a high speed. Note that Spotlight indexing runs at a higher "nice" value, i.e., it runs at a lower priority, than your interactive processes, thus once you start to use your computer the indexing takes a backseat to your interactive processes and slows down, not utilizing the same CPU load as before you began to interact with your computer. In summary, because of Spotlight indexing your computer will apparently, at random and when you are not doing anything with it, ramp up the fans's speeds. You can check if it is Spotlight indexing by looking in the Activity Monitor to see if you have "mds" and "mdworker" processes running -- these are the Spotlight indexing processes.

    There are other system processes besides just Spotlight whose running can also cause your fans to speed up their spin rates. These will also occur at apparently random times when you are not actively using your computer.


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