Hot Temps when running external monitor

[Macman756]

I have a late 2011 15: MacBook Pro hooked up to an external monitor. I know since I am using the Thunderbolt/Mini Display port it is using the dedicated 1GB AMD GFX Card, but the temperatures are crazy. On idle, with no applications open, it overs around 165 degrees. OK, fans are maybe 4,000RPM. I think that is too hot, but can live with it. Here is where it gets weird. If I walk away, and let it sit, not touch the mouse or anything, and let the displays sleep, but not the computer itself sleep, the temperatures are 200, fans are full blast at 6,000RPM. Something is working it hard. CPU usage is like 4-5%, so not CPU. Any ideas? THe laptop is on a glass desk all by itself, no blockage, not running in clamshell mode, the display brightness is at zero the the laptop display is off.

What is causing this hot temps? Thanks

 

[Macman756]

If it sits for maybe 3-4 minutes, I hear the fans crank up, wiggle the mouse and iStat says 195-205 degrees easy. Within 10 seconds the temps begin to plummet, 180, 170, 160, then stabilize around 155 and fans return to normal. I can't keep moving the mouse every 30 seconds or so, what is causing this rage on idle?

 

[inlinevolvo]

This doesn't sound right.

 

[Macman756]

This doesn't sound right.

I know. Trying to figure out what is causing this..

 

[TickleMeElmo]

Your dedicated GPU has different power states. Normally there will be one for actual idle which is where most of the transistors are power gated and effectively shut down. There is normally also a power state dedicated for processing video. Finally there is a full power state for 3D applications (such as gaming). This is independent of the clock speed manipulations that go on, since when the clock speed is reduced all the transistors are still drawing current but when the silicon enters a low power state pieces of logic are effectively shut off.

What may be happening is that if you have more than one display running the GPU is being forced into a higher power state (normally full power). And although the actual load is minimal the power draw is not insignificant. This was the case for all Nvidia cards of the Fermi generation and I vaguely recall that AMD also had the inability to send the card to a low power state if there were multiple displays connected.

 

[yusukeaoki]

Might want to get it checked out by Apple.