2018 MacBook Pro 15” - Fans Behaviour with External Display

colincjw

macrumors newbie
Original poster
Jul 31, 2013
13
0
Hi, I’ve recently got a 2 week old baseline 15” MacBook Pro (2018) and got a question about its fans.

When I’m using the Mac with its own display, everything works fine. Fans come on with heavy load, easily going down as it eases.

However, when I’ve got my single LG 4K monitor plugged in (scaled to 2560x1440), things start to get a bit weird, albeit the usual increase in temperature to ~60C.

When I’m on extended display mode, the fans tend to ramp up to ~3000 to 4000rpm idling and easily reach to ~4500rpm or higher with basic tasks like browsing via Chrome or opening a few regular programs. And when these activities are closed, the fans tend to stay on throughout, even at times when the monitor is plugged out.

When I’m on clamshell mode at the same resolution and scaling, it’s just slightly more normal in terms of fans going up and down, but that last part of the fans staying on - still persists.

Interestingly, with iStat Menus monitoring, the fans are currently at “System Controlled”. And if I switch them to “Automatic”, then back to “System Controlled”, the fans drop to its lowest idling speed and stay there. The same goes when the computer is restarted.

Things I’ve done:
  • SMC and PRAM reset
  • Safe boot
Is this pattern of behaviour normal or would it be possible hardware failure?
 
Last edited:

IdentityCrisis

Suspended
Sep 9, 2018
685
339
Hi, I’ve recently got a 2 week old baseline 15” MacBook Pro (2018) and got a questions about its fans.

When I’m using the Mac with its own display, everything works fine. Fans come on with heavy load, easily going down as it eases.

However, when I’ve got my single LG 4K monitor plugged in (scaled to 2560x1440), things start to get a bit weird, albeit the usual increase in temperature to ~60C.

When I’m on extended display mode, the fans tend to ramp up to ~3000 to 4000rpm idling and easily reach to ~4500rpm or higher with basic tasks like browsing via Chrome or opening a few regular programs. And when these activities are closed, the fans tend to stay on throughout, even at times when the monitor is plugged out.

When I’m on clamshell mode at the same resolution and scaling, it’s just slightly more normal in terms of fans going up and down, but that last part of the fans staying on - still persists.

Interestingly, with iStat Menus monitoring, the fans are currently at “System Controlled”. And if I switch them to “Automatic”, then back to “System Controlled”, the fans drop to its lowest idling speed and stay there. The same goes when the computer is restarted.

Things I’ve done:
  • SMC and PRAM reset
  • Safe boot
Is this pattern of behaviour normal or would it be possible hardware failure?
Yep, using the 4k screen it's using your integrated video card and not the intel based one. That uses more energy and heat.
 

IdentityCrisis

Suspended
Sep 9, 2018
685
339
But is it normal too for the fans to remain high even after going indle?
As long as the screen is on and connected and it has to display something to it, it will be using the "discrete video card" which creates more heat and the fans will kick up more.
 
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