Issue with 2018 15-Inch MacBook Pro overheating with external monitor

Hardware
1

I’ve been having an issue with a 2018 15-inch MacBook Pro overheating with an external monitor attached. It is very similar to what is described in this article:

I tried upgrading to Monterey and turning on the low power mode. This helps, but doesn’t completely solve the problem. One thing I don’t understand is that I will have the MacBook plugged in, but then I notice the battery starts draining. Why would it draw power from the battery when it is plugged in? Is there a way to stop this?

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I don’t think anybody’s going to be able to help you much with this, because you’ve basically just described problems that could arise using laptops (particularly high-powered Intel ones) as desktops:

  1. Your laptop might overheat. It’s trying to push more pixels than it does unplugged. If you’re using Clamshell mode with something like an LG 5K display, it would still be the case that you’re pushing more pixels than you would normally.
  2. The above would be even more true with a laptop known to be thermally constrained, as the 2016-2019 MacBook Pro models are.
  3. If your monitor cannot provide enough power to the laptop over USB-C, in situations where it’s pushing itself hard, then the laptop will start pulling from battery. If you haven’t already tried, you should also plug the brick in that came with the laptop. You’ll now be using two USB-C ports, instead of one, but at least the laptop won’t drain anymore. (If you plug in the laptop to the wall and the display, and the laptop battery still drains, I’d ask Apple about that, because that’s a real problem.)

You have my sympathies. That era of 15" MacBook Pro is what convinced me to get an iMac Pro, because the overheating was immediately obvious when I plugged a new 15" into even a 4K Ultrafine. Fans were constant, the thing was hot, and it was pretty clear early on that it would be an untenable situation.

Sorry I cannot be of further help.

3

Yeah, I just need to keep it running for a few more months when I will get upgraded to a new M1 MacBook. The strange thing is I’ve been using this MacBook for over 3 years and it’s only in the last few weeks that this has gotten much worse.

4

One thing to try is to disable “separate spaces for displays” in System Preferences > Spaces. It won’t fix whatever changed recently, but it might give you enough extra margin.

5

Get the last few months out of it by keeping it on a laptop cooler (plugged into the wall, not the laptop.)

I keep my M1 MacBook Air on an old Belkin cooling pad all the time because I like the height and the angle it sits at. I sometimes plug it in when iStat menu reports rising temperature due to heavy use during these summer months and the cooler really make a difference.

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I had no idea this existed, thanks!

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Take into account that using the external display triggers the discrete GPU, so it draws more power and more heat!. I have a pretty similar device (2018 15’’ i7 2.2 MBP) and its fans are always running these days, but it’s summer time here in Madrid, so you can figure that the thermal system needs to work more and also after several years the thermal paste may have degraded to the point of not doing its thing any more. During colder winter months the fans do not run that much (but they run as soon as I run Logic Pro, for example). As @snelly points out, there’s not much to do.

Only thing one can do is to review if there are active background processes consuming additional CPU resources. One obvious culprit could be an antivirus. But if that was the case you would also notice it with no external display connected.

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Something strange happened today, I saw that the MacBook was warming up again, so I shut it down to cool off for an hour. I left it plugged in thinking it would charge up the battery, but the battery only charged up 6% more. Does it charge more slowly when shut down?

9

I had a bad problem with my 2018 15" MBP. it got so hot that the battery bulged and they had to replace things under AppleCare…

I think it was thermal throttling issues with a bad airflow design

That worried me so much - I got rid of the laptop and now have an M1 MBP 16"

this one generally stays quite cool - with same general workflow…

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Don’t write your MBP off just yet! I have this problem too, but it’s a new problem! It’s only started with the latest Monterey update, and I have assumed Apple have made an error with an update somewhere, and also that they will fix it with the next update. I’m running a Samsung 34” monitor and a 16” MBP and it was fine before the update.

In the meantime, I don’t know if you want to, but turning off my MBP monitor seems to fix the problem (so in my case I’m just working off one screen). Hopefully Apple will fix it soon.

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Right, it just started happening a couple of weeks ago. But I was using Big Sur when it happened. I upgraded to Monterey hoping that would fix it, but alas it does not.