2018 Macbook Pro Fan always runs when USB-C has HDMI plugged in

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2018 Macbook Pro Fan always runs when USB-C has HDMI plugged in

For whatever reason my macbook fan always runs at what seems to be full power and the computer gets very hot when I have my USB-C hub plugged in with the HDMI connected to my external monitor. What is strange is that I was able to avoid this in the past when I would change the hub to a different USB-C port on my macbook. Now, no matter which one I plug into the same issue occurs. The problem here isn't that the fan is just noisy but the computer seems to really heat up. I always check the activity monitor and nothing is out of the ordinary. If i was just doing word processing this wouldn't bother me, but I am an audio engineer and when I am working in logic a lot of the heavier projects tend to kick the heat into overdrive and as a result sometimes my computer starts to do strange things, like software stops working right or USB ports start malfunctioning. If I do the same thing I normally would do but just have the laptop with no external monitor everything works perfectly fine. This sounds like a massive bug.

OSX 10.13.6

Anyone have any ideas?

Posted on Jul 30, 2019 5:56 PM

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Answer 1

Top-ranking reply

Grant Bennet-Alder

Level 10

141,793 points

Jul 31, 2019 8:32 AM in response to CoFerreira

Your Mac features Dual graphics. There is built-in GPU that is used for 'ordinary' work, and a more powerful Discrete GPU that is used for more demanding work. MacOS switches back and forth as needed.

The hardware is wired so that when you make a direct connection to an External display, the Discrete GPU is activated and used for everything. That uses more power.

If you use a simple adapter to a 'legacy' interface {HDMI, DVI, VGA} your Mac sends the entire screen out every 60th second. This is referred to as the 'heartbeat' refresh required by Analog CRT displays. That is a lot of data and things get hot. If you use a modern DisplayPort family interface, the screen has a display buffer and is sent only the changed data. When the screen stops moving, the link goes nearly quiet, and your Mac generates less heat. A direct Thunderbolt connection to a display uses DisplayPort alt mode, a subset of ThunderBolt, to work in an nearly identical way.

If you connect through a Mult-funtion Dock AND use a "legacy" interface {HDMI, DVI, VGA} many docks do not convert the existing signal. They instead use software to create a "simulated" display by creating a display buffer in RAM, (not providing graphics acceleration at all) and send the display data out to the Dock using a slower connection. This software and the custom chips that provide the "legacy" ports is made by DisplayLink. Recent changes to MacOS security have meant some scrambling by DisplayLink to keep up.

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Answer 2

Jul 30, 2019 6:52 PM in response to CoFerreira

When you are running "legacy" displays, every bit on the screen is sent from the Mac display buffer every 1/60th second. That takes a lot of switching, and things get HOT.

A DisplayPort display just sends the changes. if the picture stops changing, the link goes nearly quiet.

Get yourself a DisplayPort display and live happily ever after.

If this is a dual Graphics MacBook pro 15-in, the external display uses the Discrete graphics chip.

If you were using a dock before, but are using a direct connection now, that changes the way the Mac responds. I can explain, but it takes quite a bit of explaining, so post back with the exact before and after configurations.

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Answer 3

Jul 31, 2019 8:57 AM in response to CoFerreira

CoFerreira wrote:

Sounds like apple really screwed here. They give the laptop a secondary graphics card to do all the fancy work and instead of it doing some easy things to decrease load on the machine it ends up adding a ton of wear and tear, causing issues.

On the contrary, Apple has produced a MacBook that can drive multiple displays with graphics acceleration making the editing of video with real-time special effects possible on a lightweight portable computer.

Your choice of "legacy" display with HDMI generates more heat. If you used a DisplayPort display or ThunderBolt display rather than a TV set, it would run cooler.

Just for the record, the fans in your MacBook pro are running whenever it is on and not sleeping. They just ramp up into the audible-and-annoying range when measured temperatures inside your Mac require more heat removal.

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Answer 4

CoFerreira Author

Level 1

17 points

Jul 31, 2019 9:25 AM in response to CoFerreira

It appears my monitor does have thunder bolt 2, but on some sites it says thunderbolt 2 and displayport interfaces. a quick bit of googling shows me that they are not the same even though they are the same interface port.

I am guessing that I cannot get a USB-C to displayport cable/adapter and use it? I must get a usb-c to thunderport 2 adapter and then from there a thunderbolt 2 cable? I am googling for how to obtain this configuration and it doesn't look like there is a simple solution for USB-C to thunderbolt 2...but a lot of cables/tech that is usb-c to displayport.

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Answer 5

CoFerreira Author

Level 1

17 points

Jul 30, 2019 9:45 PM in response to Grant Bennet-Alder

Thanks so much for the info. I have a few more questions is you would be willing to answer.

I dont have a display port only usb-c assuming this is apple semantics and its just a driver protocol meaning if i get a displayport display it uses some fancy apple driver and the pain goes away?

my macbook has an independent graphics card, it does not use shared memory...is this the same concept as dual graphics? Wether it does or doesn't what impact does this have?

Ive always used a hub of some sort because its USB C there is no way to not use a hub or adapter to run anything that isnt also usb-c. Unless i get a usb-c monitor there will never be a direct connection. Again, what impact does this have or not have?

thanks!

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Answer 6

CoFerreira Author

Level 1

17 points

Jul 31, 2019 8:49 AM in response to Grant Bennet-Alder

Sounds like apple really screwed here. They give the laptop a secondary graphics card to do all the fancy work and instead of it doing some easy things to decrease load on the machine it ends up adding a ton of wear and tear, causing issues. Well, good to know. Maybe I'll look into investing in a monitor with a proprietary thunderbolt/displayport interface in the future, only for apple to then finally not do silly things like this. To be honest this sounds horrible as my last macbook had HDMI built in and never had this issue. Bad move on apples part.

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Answer 7

CoFerreira Author

Level 1

17 points

Aug 11, 2019 8:24 PM in response to CoFerreira

hey Grant, thank you so much for the advice.

I purchased a USB-C to display port cable, This one on amazon: https://www.amazon.com/gp/product/B01J6DT070/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

Apparently that has had very little effect on this whole thing. It is still causing my fan to run extremely hot when plugged in. In fact, it appears that 50% of the time when I am running a project (in logic) that one of my CPU cores is maxed out at 100%...even when doing nothing (sitting idle with the program open). This is really frustrating as my last macbook with dedicated HDMI port worked just fine under these circumstances. Spending almost $5k for a new laptop that performs poorly with my external monitor is beyond frustrating. This MUST be some kind of software / driver issue that Apple needs to solve for. I doubt im the only person with this problem.

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Answer 8

Jul 31, 2019 6:30 AM in response to CoFerreira

Exactly which MacBook pro 2018 by screen size, Touch Bar or no, and processor speed?

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Answer 9

CoFerreira Author

Level 1

17 points

Jul 31, 2019 7:06 AM in response to Grant Bennet-Alder

15 inch with touch bar 2.9ghz 7th gen.

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Answer 10

Jul 31, 2019 9:45 AM in response to CoFerreira

what display Make&model?

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Answer 11

CoFerreira Author

Level 1

17 points

Jul 31, 2019 10:03 AM in response to Grant Bennet-Alder

LG 34UC87M

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Answer 12

CoFerreira Author

Level 1

17 points

Jul 31, 2019 10:41 AM in response to Grant Bennet-Alder

awesome thank you so much. I really appreciate the info.

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Answer 13

CoFerreira Author

Level 1

17 points

Aug 11, 2019 8:54 PM in response to Grant Bennet-Alder

Ok i will run a test at some point tomorrow or the next day and send it over. thanks!

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Answer 14

Jul 31, 2019 10:29 AM in response to CoFerreira

That display features inputs:

(2) HDMI

(1) DisplayPort [Full size]

(2) Thunderbolt-2 marked with the thunderbolt symbol

on your 2018 MacBook Pro :

• From a ThunderBolt-3 port you could use the Apple ThunderBolt-3 to Thunderbolt-2 adapter. This works as long as the display is a genuine Thunderbolt display, which this display claims to be.

• From a ThunderBolt-3 port you could use a third-party DisplayPort adapter, rated for "4K"

If Apple had decided to build a DisplayPort "multi-port adapter", it would be very much like this one:

Monoprice Select Series USB-C DisplayPort Multiport Adapter # 33042 $27.80

This one without the extra USB-C and USB-A is also available for less:

Monoprice Select Series USB-C to DisplayPort Adapter # 13234 $17.09

.

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Answer 15

Aug 11, 2019 8:40 PM in response to CoFerreira

Let's take a look at where your computer resources are being spent. Download Etrecheck, set its preferences to "allow Full Disk Access" and run. Its report can be posted to a pastebin.com posting (and post a link here) or to a reply on the forums. No personally-identifiable information is disclosed.

Using EtreCheck to Troubleshoot Potential… - Apple Community

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2018 Macbook Pro Fan always runs when USB-C has HDMI plugged in

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