Macbook Pro runs lot cooler in clam-shell mode

[ParagJain]

Hi - just wanted to verify if this is an expected behaviour .

I have a 2015 version of Macbook pro - connected with LG UHD external monitor.

Past few days, i am seeing that when i use the macbook and the external monitor, it runs very hot, sometimes hot enough to feel uncomfortable touching the function keys. CPU temp goes higher than 75, The underside also is super hot, can hear the fan noise.

Doing similar tasks but running in clamshell mode, it runs lot cooler and fan hardly touches 2000 rpm. CPU temp stays 51 to 65

99% of my tasks are browser based - documents, video streaming & browsing

Note - didn't observe this earlier as it was always in clam-shell mode; Now that lockdowns are relaxing a bit, i will be heading back to office and hence, i started observing this recently.

Is this expected ? thx.

 

[reasonrulaz]

Yes, because if your mbpro has dedicated graphics, it's activate for drive external monitor and device display simultaneously while lid open .. It's cause a lot of pixel to process, so produce heat.. Clamshell mode reduce CPU+GPU workload.. Same situation also valid for internal graphics only devices.. Especially dedicated graphic units activated for usual light usage scenarios for external display mostly unnecessary..

But i'm worry about airflow when i'm use Clamshell mode. I thought that heat maybe trapped between display and keyboard..

 

[ParagJain]

But i'm worry about airflow when i'm use Clamshell mode. I thought that heat maybe trapped between display and keyboard..

Using in Clamshell mode, I keep the heat-sink vents upside, when I put my hand, I feel that place as warm and sometimes, I feel warmer air blowing out..again, its just warm so I don't worry too much.

Thx, your observation above helps .. at-least for now, I have not much to worry then.. appreciate it.