2015 15" MacBook Pro w/ AMD Radeon R9 M370X loud fan.

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Level 1

8 points

2015 15" MacBook Pro w/ AMD Radeon R9 M370X loud fan.

Hello.

I have a 2015 15" MacBook Pro w/ AMD Radeon R9 M370X and the fan is often loud. Sometimes it will kick on for a about a minute then go off, then repeat a few minutes later. It might only be the left fan? The left side seems warm, but not really hot.

Is this normal with the model with dedicated graphics? My previous MacBook was a Late 2013 13" and that fan almost never kicked on even with heavy usage.

I ran an Apple Hardware Test which found nothing, and reset SMC which didn't appear to help.

I am often plugged into my 27" Apple Cinema Display, so dedicated graphics will be in use when this happens. But it does also often happen when I am not asking a lot of the system and I am not plugged into an external display.

I just got off the phone with Apple and they want me to take it into a store. The tech told me to boot into Safe Mode to see if the issue persists. I have been working in Safe Mode for about 15 minutes now. Fan is audible and constant, not really really loud but it's going constant. It's not revving up and down like it does during a normal boot nor does it feel hot, just a little warm. All that is is currently running right now is Activity Monitor, Messages, Mail, Safari and Mac is currently backing up to Time Machine via ethernet. Also useful to mention, the MacBook is well ventilated sitting on top of a M Design Rain Stand in clamshell mode now.

I'm not sure if this is normal due to the dedicated graphics card or if I am having an issue with my fan?

MacBook Pro (Retina, 15-inch, Mid 2015), macOS High Sierra (10.13.2)

Posted on Jan 21, 2018 9:33 AM

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Answer 1

Jan 21, 2018 9:47 AM in response to DBirdMcG

The interfaces for external displays are wired ONLY to the Discrete graphics chips on Dual-Graphics Macbook Pro.

The Mac runs the fans in a feedback loop based on measured temperatures inside the Mac and inside the chips. Graphics-intensive work is expected to boost fan speeds.

Running with the lid closed disrupts the intended cooling. You cannot effectively use the metal top-cover (keyboard level) to dissipate accumulating heat. Even of you choose to not use the built-in keyboard, you can still use the built-in display in conjunction with an external display in either 'Extended Desktop' mode or 'Displays have separate spaces' mode.

You could even just put Activity Monitor on the built-in display and ignore it otherwise.

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Answer 2

Jan 21, 2018 10:31 AM in response to DBirdMcG

I think the way DisplayPort works may explains the behavior. When the screen changes, the rasterization Hardware reads the screen buffer to obtain the information about which pixels must be lit up, and looks up what color information should be sent as well.

On a DisplayPort display, that produces a huge rush of activity in the fast and hot Display Hardware in the Mac, and likely a spike in heat generated. Then the fans would kick up a notch to get rid of the heat. Then it quickly tapers off if the picture is stable, because only the changes will be sent, and the cable goes mostly quiet.

In contrast, i expect if you had a display with a legacy interface, changing the screen would produce a rush of activity followed by the "heartbeat" re-painting, 60 times a second. The fans would kick into high, and never stop.

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Answer 3

Jan 21, 2018 10:20 AM in response to DBirdMcG

Does your external display have a DisplayPort input?

DisplayPort displays are by far the lightest load on the graphic subsystem, because once the screen image is stable, there is no 60Hz "heartbeat" of repainting the screen, and all that fast hot electronics can cool off.

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Answer 4

Jan 21, 2018 10:44 AM in response to DBirdMcG

If you take a look at Acuity Monitor, especially the CPU pane, there seem to be HUNDREDS of tasks with a thousand or more threads inside macOS, all doing stuff at varying times. If a whole bunch of them accidentally line up, your Mac could have a whole lot to do -- for a very short while.

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Answer 5

DBirdMcG Author

Level 1

8 points

Jan 21, 2018 9:53 AM in response to Grant Bennet-Alder

So you think it is normal then when connected to a monitor for this to happen? But I do also get issue when I am not plugged into a monitor and the system is not using the high performance graphics.

I don't often run graphics intensive applications, note the items I listed that are running while the fan is being loud when I typed this up.

I have heard the Mac cools itself just fine in Clamshell mode. But I have also heard otherwise. Also, wouldn't opening the lid ask more of the system? Because then it is powering two displays? In Clamshell mode the system is only powering the external display.

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Answer 6

DBirdMcG Author

Level 1

8 points

Jan 21, 2018 10:35 AM in response to Grant Bennet-Alder

Everything you are saying makes sense... I do recall reading DisplayPort is superior to DVI, VGA, perhaps even HDMI? etc.

But my fans will occasionally kick on when I'm not plugged into a display and my machine is not demanding the high performance GPU too...

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Answer 7

DBirdMcG Author

Level 1

8 points

Jan 21, 2018 10:46 AM in response to Grant Bennet-Alder

Makes sense. I will keep watching Activity Monitor. It most often appears to be mdworker which I believe has something to do with Spotlight.

Thank you for your input.

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Answer 8

DBirdMcG Author

Level 1

8 points

Jan 21, 2018 10:20 AM in response to Grant Bennet-Alder

Yes. It is the Apple Cinema Display, the model just before the Thunderbolt Display. It has a Display Port and a USB cable for the speakers, hub, camera etc.

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