Oh yeah, I forgot about the graphics.

I had (and still have) a 4k external monitor. Naturally I wanted the MBP to drive the monitor with a resolution that took advantage of all the pixels. Unfortunately with most monitor settings the GPU power consumption would produce enough heat to run the fans even if the rest of the system was completely idle! If I set the output to full HD the GPU would cool down and the fans would turn off. But full HD on a 4k monitor is a waste.

It was very strange. I could drive the monitor at 4k but with the image upside down, and the power consumption would be low. But flip the image right side up and it would run hot and turn on the fans.

It took a couple weeks of fiddling, but I finally found a combination of refresh rate, resolution, image orientation (right side up!), and cabling that let me drive the monitor at high resolution without running the fans. What a pain.

(I used iStat menus to monitor GPU power consumption. At “good” settings it consumed about 5w. At “bad” settings it would consume 17w. At a bad setting you could immediately see the various temperatures go up and the fans spinning up to compensate.)