MacBook Pro 15inch mid 2014 - Fan issue with 4K Display

Discussion in 'MacBook Pro' started by klogg, Jul 20, 2017.

  1. klogg macrumors member

    Oct 17, 2012
    I'm having an issue with MacBook Pro 15inch mid 2014, with dedicated GPU. When I attach my dell 4k display, the fans starts working almost immediately, they are not at 100% but they are loud, and its noisy, even though the machine is idle. I'm using OS X 10.9.5.

    Is this normal? Is there anyone else using same machine and 4k display that can confirm this?

  2. Moriarty macrumors 6502

    Feb 3, 2008
    Power consumption increases when using external displays for two reasons. First, it always uses the dGPU. So even in clamshell mode, it's enough to keep the system warm.

    Second, the idle clocks of the GPU in multi-monitor mode are very high, pushing power consumption even higher. It's a quirk that happens when the resolution / refresh rates are different. If I turn on mirroring with my 1920*1200 external display on my 2012 rMBP, total system power consumption drops from about 30 W to 20 W.

    It's a stupid problem, and one that I have heard doesn't happen with AMD cards. The best way to minimize power consumption is to use clamshell mode. Then you're only taking the hit for dGPU use, and not also for stupidly high idle clock speeds.
  3. klogg thread starter macrumors member

    Oct 17, 2012
    Wow, thanks man, so in clamshell mode, the fan noise is lower a lot. Do you think this will not hurt macbook, because I don't see a way for the air to get out?
  4. Moriarty macrumors 6502

    Feb 3, 2008
    The exhaust air from the fans can still escape from the vents. Just look at the back of the laptop below the hinge and you can still see them and feel air escaping.

    I don't think that airflow is affected significantly. The laptop will run much cooler, so if you don't really need to use the internal display then clamshell is the way to go.

    If you have never cleaned inside the laptop, I suggest you get one of the special screwdrivers (iFixit sells them) and clean the dust out of the fans / heat sinks. That will also help.

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