The situation:

I work in a very quiet office using MBP Spring 2011 with an i7. The problem is that when I put an intense but short workload for a few seconds on the CPU the fans spin up heavily, disturbing me and especially my office mates.

I elevated the MAC to get some air flowing under the body but that was not sufficient.

So I found a solution to limit the fan speed, currently limiting it to 3500 by using:

cd /Applications/smcFanControl.app/Contents/Resources
./smc -k F0Mx -w 36b0
./smc -k F1Mx -w 36b0

The question:

How dangerous is doing this?

My current line of thinking is: the cooling is now insufficient for intense long workloads. But if the CPU gets too hot it will just throttle or at worst the MBP might shut down, but nothing worse should happen. Many Laptops have dusty or broken fans and they don't burn out their CPUs either.

Is this a reasonable assumption or am I risking real damage here?

  • If you run these intense tasks often, I would expect this to shorten the life of your machine. I'm no expert though – JoshRagem Oct 29 '12 at 15:58
  • Could you possibly fix this the other way by doing something to reduce the workloads in exchange for a slightly longer runtime? Perhaps there are tools to help here: apple.stackexchange.com/q/55964/1209 – rjmunro Oct 29 '12 at 17:39
  • @JoshRagem: yeah, I forgot to mention this: I am aware that now that the MBP is running it hotter, this theoretically reduces the life expectancy a bit. I do not care if the life expectancy changes from 10 years down to 8 or so, I am worried about acute CPU-death. – Raimo Ihle Oct 29 '12 at 23:01
  • @rjmunro: yes I have looked that question before: can't use gfxCardStatus to force use of integrate GFX, cause external monitor is connected, also I'm pretty sure it's CPU not GPU causing the heat. CPULimit would be a bit difficult to use, cause it is a bunch of different programs that seem to be causing it. Coolbook will not work on Lion. Forgot to mention this too: Runtime is not important, the MBP is not running on battery, but on main power. – Raimo Ihle Oct 29 '12 at 23:12
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    Is there any way you can alter your office environment? It sounds to me like if something like spinning up fans disturbs your office mates, then there must be a lot of other mundane things that would do the same, and you'd lose productivity avoiding those things. – Reid Oct 30 '12 at 18:23

Some quick research says that the i7 processor starts to throttle itself if the temperature range gets too high (around 91C) so you shouldn't have to worry about it provided your CPU temp stays less than that. Mostly the fan speed is trying to keep it comfortable on your lap as best it can - monitor your temperature during one of these "intense sessions" and see if it approaches that threshold - if it doesnt, and stays more on the order of 60C, you're fine as far as short term CPU viability


  • This does not take into account all the other components in the MacBook. – Gerry Oct 30 '12 at 17:17
  • @Gerry true - but the OP was specifically asking about CPU - it's reasonable to assume as well that other components will be slower to heat up (since CPU heat is being diffused, and according to the OP is generating the most heat) and most components in the newer macbooks wouldn't be sensitive to that level of temperature - SSDs, for instance, are very heat tolerant. in any case, going through all this over a burst of fan noise seems silly to me, but hey – JRaymond Oct 30 '12 at 22:48

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