External Monitor Increasing Mid 2015 Macbook Pro Temperatures

[corneduring]

I only recently purchased a 2nd hand Mid 2015 Macbook Pro with both integrated and dedicated graphics chips. Idle temperatures were about 50 C. I then took the macbook to get professionally serviced where they cleaned it out and replaced the thermal paste. The idle temperatures then dropped to the low 30's C. When I really let it idle for a while it even drops below 30 C. After actually using the machine for a while the temperatures are in the low 40s C.

However, I noticed that the moment I decide to connect the macbook up to an external monitor via HDMI the idle temperatures immediately starts to rise from the low 30s C to the low/mid 50 C. I would probably imagine to see the temperatures rise after connecting an external monitor because of the extra graphical power needed, but I didn't think it would cause such a big increase in the idle temperatures? Especially if you consider the fact that during my whole troubleshooting/testing process the external monitor literally is only showing the desktop for the entire time.

Does anyone have any advice on this? Is this normal behaviour. Is there anything I can do to improve this? I have tried many things like resetting the NVRAM, resetting the SMC, booting into safe mode and then into regular mode afterwards etc. Could it be something weird like the mac switching to the integrated graphics after connecting an external monitor?

It's not that the macbook is "overheating" by any means, but it might do so if I decide to actually load the mac with more heavier tasks after connecting an external monitor.

All help is appreciated. Thanks.

 

[jav6454]

The reason might be that the dGPU in that revision is taking over due to the resolution of the external monitor.

 

[corneduring]

The reason might be that the dGPU in that revision is taking over due to the resolution of the external monitor.

I checked in the settings that the dGPU is being used for both the built-in display and the external 1080 FHD display. Should it not do that and is it even something that can be changed manually?

 

[jav6454]

No idea, if the dGPU is turned on, it's due to the OS thinking it is required.

 

[corneduring]

Still open for any other input...

 

[DeltaMac]

What happens with the temps if you actually "load the mac with more heavier tasks after connecting an external monitor"? That's just another test, using whatever software load that you might expect
I expect you will find out it will heat up more. Too high, and your CPU/GPU will protect itself to some degree.
Or, you may discover that the heat will level off at some point, no issues, other than running hot, which you can probably mitigate to some extent.
You could also try alternate video connection, such as DisplayPort, if the display has that as a choice.
And, if your external display is HDMI-only, you can try MiniDisplayPort to HDMI (different paths might be enough to result in somewhat lower temps - worth a try if you get concerned about the heat (higher than maybe 85-90 C. under load) You should also make sure that the fans are ramping up when the heat is there ( >70 C. )

 

[corneduring]

What happens with the temps if you actually "load the mac with more heavier tasks after connecting an external monitor"? That's just another test, using whatever software load that you might expect
I expect you will find out it will heat up more. Too high, and your CPU/GPU will protect itself to some degree.
Or, you may discover that the heat will level off at some point, no issues, other than running hot, which you can probably mitigate to some extent.
You could also try alternate video connection, such as DisplayPort, if the display has that as a choice.
And, if your external display is HDMI-only, you can try MiniDisplayPort to HDMI (different paths might be enough to result in somewhat lower temps - worth a try if you get concerned about the heat (higher than maybe 85-90 C. under load) You should also make sure that the fans are ramping up when the heat is there ( >70 C. )

Thanks for your insights. Ordered a mini displayport to hdmi cable today, so will be testing that out tomorrow. From the answers I'm getting so far via other sources and this thread it seems like a lot of people are basically saying that I shouldn't worry much about the temperatures unless they start to constantly approach the 80 C+ range?

The initial reason for me trying to find help online for this "issue" I'm having was just because of the big increase in idle temperatures between having and not having an external monitor connected just didn't make sense to me, regardless of what the actual temperature ended up being. It's the 20 C increase after just connecting an external monitor that botheres me.