2017 15" MBP fans run w/external monitor

[djc6]

Four months ago, I got a 15" 2017 MBP and two LG 27UD58P-B 4K monitors. Monitors are connected via passive USB-C to displayport cables.

The week or so, my fans run nonstop at what sounds like full speed. If I unplug the external monitors, within a few seconds the fans slow down dramatically. This wasn't an issue before, so I'm trying to sort out what changed recently.

I use this setup for work - I have Chrome, Firefox, Slack and Terminal open - thats it. The fans still run at full tilt when I close all applications and just display static desktop.

I've tried resetting SMC, NVRAM multiple times to no avail. Activity Monitor shows 94% idle CPU most of the time, nothing is using lots of CPU. I have less insight into the GPUs - I installed iStats Menu and XRG to monitor GPUs - they basically measure frame rate, amount of time CPU is waiting on GPU, and VRAM urilization. Only odd thing I've noticed is that I'm usually using 95% VRAM on Radeon and nothing on the Intel GPU. I was expecting something on Intel GPU - why put all three displays on one GPU?

Curiously, if I unplug the monitors and plug them back in, the Radeon VRAM utilization drops to like 30% and stays there for 10-15 minutes, then spontaneously jumps to 95% utilization.

Maybe it was 10.13.3 update I installed a week ago that caused this problem? Roughly same time this started.

 

[shaunp]

I had this issue on a 2011 MBP and Apple couldn't(wouldn't) find a fix until I showed them video evidence. They didn't even plug in an external monitor as part of their tests because apparently their diagnostic software is all-knowing. They apparently replaced the thermal paste, but I'd had enough by then and got rid of the machine. A few months later they publicly acknowledged the problem with the 2011 MBP and had a replacement programme.

I wouldn't rely on updates, I would gather video evidence of the issue and take and the laptop into Apple for repair/replacement.

 

[djc6]

So this is interesting. I have one display plugged into rear left usb-c port, the other rear right usb-c port.

If I plug official apple power adapter into front left usb-c port - the fans roar. iStats Menu shows "Thunderbolt Left Proximity" quickly approaching 160F.

If I plug official apple power adapter into front RIGHT usb-c port, no fans. Temps for "Thunderbolt Left Proximity" and "Thunderbolt Right Proximity" remain below <120F

So I have same devices plugged in, just rearranged them and was able to achieve silence. Any clue why?

 

[Falhófnir]

I have heard the fans on the 15” are always actually on due to the 45W processor requiring some degree of constant active cooling (or at least that has been the case for past models). Usually they are just not detectable as they are running at low rpm. Connecting an external monitor will put more strain on the system which will cause the fans to run up accordingly. What you describe does sound significantly abnormal that you probably should take the issue to Apple and see what they have to say though. I wouldn’t expect fans to spin up high just for the monitor being connected...

 

[Fishrrman]

djc6 wrote:
"So I have same devices plugged in, just rearranged them and was able to achieve silence. Any clue why?"

Best advice I can give:
"Go with what works for you. Ignore what doesn't."

 

[Samuelsan2001]

Four months ago, I got a 15" 2017 MBP and two LG 27UD58P-B 4K monitors. Monitors are connected via passive USB-C to displayport cables.

The week or so, my fans run nonstop at what sounds like full speed. If I unplug the external monitors, within a few seconds the fans slow down dramatically. This wasn't an issue before, so I'm trying to sort out what changed recently.

I use this setup for work - I have Chrome, Firefox, Slack and Terminal open - thats it. The fans still run at full tilt when I close all applications and just display static desktop.

I've tried resetting SMC, NVRAM multiple times to no avail. Activity Monitor shows 94% idle CPU most of the time, nothing is using lots of CPU. I have less insight into the GPUs - I installed iStats Menu and XRG to monitor GPUs - they basically measure frame rate, amount of time CPU is waiting on GPU, and VRAM urilization. Only odd thing I've noticed is that I'm usually using 95% VRAM on Radeon and nothing on the Intel GPU. I was expecting something on Intel GPU - why put all three displays on one GPU?

Curiously, if I unplug the monitors and plug them back in, the Radeon VRAM utilization drops to like 30% and stays there for 10-15 minutes, then spontaneously jumps to 95% utilization.

Maybe it was 10.13.3 update I installed a week ago that caused this problem? Roughly same time this started.

The video output on the 15 inch runs through the dGPU only I'm afraid, you cannot use the igpu for external screens period.

It does sound like a bug in the software, I haven't heard too much on this though so maybe an OS reinstall will sort you out.

 

[bhatiak]

Well - the fans on my 2017 nTB get pretty loud if I'm doing a little bit of multi-tasking with a measly 1080p plugged in. Pretty stupid if you ask me lol.

 

[djc6]

So the laptop belongs to my employer. I asked IT dept, they gave me a second laptop (brand new) with identical specs to tinker around with. I used Disk Utility (in recovery mode on new laptop) and target disk mode on old laptop to perform an exact byte for byte copy of the SSD onto new laptop. With the software identical, the new laptop does not have fan issue when I plug power into left thunderbolt ports along with both 4K monitors. iStats Menu shows Left/Right thunderbolt proximity sensors at near identical temperatures.

I am wondering if I caused the problem on old laptop by resetting SMC/NVRAM. I was trying to address an issue where both external displays are hard to wake from sleep. The new laptop has similar issue, if I press touch ID to wake laptop from sleep, its hard to get both external monitors and internal display to come back to life sometimes.

 

[4RunnerHeaven]

When you hook up external monitors to your MBP , it runs off the Radeon card instead of the integrated one. Those get hot and require a lot of cooling. Mine doesn't run on full, but they do run, and it helps to leave the lid open.

 

[djc6]

When you hook up external monitors to your MBP , it runs off the Radeon card instead of the integrated one. Those get hot and require a lot of cooling. Mine doesn't run on full, but they do run, and it helps to leave the lid open.

I basically use my laptop as a desktop replacement. Its always sitting with the lid open on a Rain Design mStand Laptop Stand

 

[creechy]

When you hook up external monitors to your MBP , it runs off the Radeon card instead of the integrated one. Those get hot and require a lot of cooling. Mine doesn't run on full, but they do run, and it helps to leave the lid open.

I don't entirely believe this reason. I have noticed the same problem as djc6 even with a single 4K USB-C monitor with lid open. Amusingly, if I connect an older MacBook Pro (Retina, 15-inch, Late 2013) to the same monitor (via DisplayPort) it does not appear to run as hot.

 

[smirking]

So I have same devices plugged in, just rearranged them and was able to achieve silence. Any clue why?

I remember reading someone on MacRumors had figured out why this was. I can't recall what the reasoning was, but you're not imagining this. There is a very real reason why the fans are running when the power draw is from one port vs another. I've noticed this too in my 2016 MBP. It runs much hotter when I get power from my left side ports.

 

[creechy]

I remember reading someone on MacRumors had figured out why this was. I can't recall what the reasoning was, but you're not imagining this. There is a very real reason why the fans are running when the power draw is from one port vs another. I've noticed this too in my 2016 MBP. It runs much hotter when I get power from my left side ports.

I started wondering if it had to do with both providing power and video signal at the same time. And for me, I'm pretty sure I've seen it with the right ports as well. Strange thing is that its not consistent. This morning, have the same apps running, and everything is nice and cool and quiet. Even though battery is at 81% and charging. Some days even with 100% battery fan is spinning all day.

 

[Honza1]

High fan speed due to external monitor(s) is not necessary. I am now running my 2017 MBP (3.1GHz i7, Radeon Pro 560 4MB) with 3 displays running :
1. internal display set to HD resolution
2. 4k display connected through USB-C to Display port (right hand side)
3. HD display connected through USB-C hub (with Display port) (right hand side)

All three (yes, displaying static windows, this is office stuff) at the same time and all fans are at their base sped (2k rpm).
CPUs (at idle) are around 60C, GPU also around 60C, Thunderbolt proximity on right hand side is 62C. All is actually nice and quiet. The system total power seems to be 28-40W while typing this.
Now, if I start something CPU intensive, they will spin up. But the base load does not require even in this case any higher fan speed than base 2k.