When does the fan actually increase speed

Discussion in 'MacBook Air' started by usmaak, Aug 26, 2012.

  1. usmaak macrumors regular

    Apr 13, 2012

    Today while I had my MBA closed up and working off of a monitor, my Roboform on Safari sort of went wacky and pegged the processor. The only reason I knew this is because Safari locked and I couldn't do anything. So I switched over to iStat, and it had my temperature at 202 degrees Fahrenheit. If my conversion is correct, that's 94 degrees Celsius. But the entire time that this was going on, the fan in my system was running at 2000 RPM. It never picked up speed even a little bit. Given how hot the computer got, shouldn't it have increased speed to compensate for the heat?
  2. filmbuff macrumors 6502a


    Jan 5, 2011
    My fan starts picking up when the CPU gets to 150F, but it really speeds up at 180+F. Then the fan stays at a high speed and the CPU temp comes back down to 170 even when it is running at full tilt.
  3. usmaak thread starter macrumors regular

    Apr 13, 2012
    So the fan not spinning up when it gets to 200 fahrenheit is definitely abnormal?
  4. usmaak thread starter macrumors regular

    Apr 13, 2012
    Just to clarify, this is a 2012 MBA with an i7.

    To further check out the issue, I downloaded a stress test, and ran it on the computer. It got up to 205, and then the fan started to ramp up. It got all the way up to 4500rpm before I stopped the stress test. It kept the temperature between 205 and 211. The heatsink temp never got above 115.

    I then decided to give it a try on my wife's 2012 MBA with an i5. The results were actually very similar. No fan activity above 2000rpm, until I hit around 200 degrees. Then the fan started to spin up. It kept the temperature between 195 and 202. The fan spun up to around 4000rpm before I shut the test down.

    So it seems like maybe these are acting like they should act. I'm not sure why the computer would be allowed to get so hot before something is done about it, and I'm not sure why the fans only ramp up to keep it at a max temp of between 200 and 210 fahrenheit. I'm also not sure why there's a ten degree difference between the i5 and i7.

    I'm still trying to decide whether to keep or return. And advice or practical experience would be very helpful.
  5. macneubie macrumors regular

    Aug 8, 2011
    check under Activity Monitor to see if any apps are consuming significant CPU clock cycles.

    My 2012 i7 MBA rpm shot up to 4500+ when I installed SplashTop Streamer on it, the moment i killed it, the CPU temp dropped from 70+ deg C to 40+, fan speed dropped slowly to <2k.
  6. usmaak thread starter macrumors regular

    Apr 13, 2012
    I'm not talking about a runaway process. Originally I did have one. It was Safari, and I killed it. The problem I had with it was even though the computer was at 202 degrees, the fans hadn't spun up at all. They were still rotating at 2000rpm. So I tested when they'd spin up using a CPU stress program. It got up to 205 before the fan started to increase. And it only increased slowly. It kept my processor right around 210 the entire time. That seems to be around the thermal max for this CPU. So I tested my wife's machine, and her's did the same thing, though the temperature at which the fan started to increase and the temp at which the fan kept the CPU was around 200. The only difference between the two computers is that her's is an i5, and mine is an i7.

    I was just trying to determine if it was normal. It seems excessive to allow a CPU to get that hot before using the fan to combat the temp. But I am coming from a Windows PC world, and I know nothing about Macs or laptops. If I search online, all I find is a ton of references to computers running hot and fans running excessively.
  7. macneubie, Aug 27, 2012
    Last edited: Aug 27, 2012

    macneubie macrumors regular

    Aug 8, 2011
    Speaking of that, I do have the same observations in iStat when the CPU temperature got unusually hot while the fan is just running at its minimum 2000rpm speed. Took a while before the fan runs up to >3500 rpm...

    I suspect the temperature sensor might not be mounted on the CPU die, instead it's mounted some distance away, e.g. the heatsink, so it takes a while for the heat conduction to reach the sensor to register a trigger in spinning up the fans.

    hence this might explain for the delayed spin-up and spin-down when the cpu temp gets too hot and cools down. the heatsink is soaking up lots of heat and takes time to dissipate the heat from the cpu. this might be good practice though, as the user would hear gradual increase/decrease in fan noise and not the sudden step-changes in fan noise as Apple wanted users to experience.
  8. borisiii macrumors 6502

    Jul 4, 2010
    Apple laptops have always tended towards quieter operation at the expense of higher running temperatures, so what you are seeing is most likely normal.

    However, if you want it to run cooler (but louder), you can use smcFanControl.
  9. usmaak thread starter macrumors regular

    Apr 13, 2012

    I did notice that the temp sensor on the heat sink never got above 115 degrees.

    It just seems like a very bad practice to let a CPU get up to 200+ degrees. I thought that the max on these things was 100 degrees Celsius. On my Windows desktop machine, I have to try hard to get it up to 175 degrees, and the fans are spinning like crazy. So a CPU at 210 degrees when running full on only one core just seems totally crazy and unacceptable to me. I guess that this is going to take some getting used to.

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