iMac excessive GPU heat when using a second display

Question

Without a monitor connected (via Thunderbolt/mDP) to my iMac (2011, 3.4 GHz, 6970M 2GB), iStat Menus reports the GPU is using ~15 watts, and has a temperature of 60c. With one connected, it uses ~35 watts, and is ~80c. Both of these are when idling.

Regardless of it pushing an extra 1920x1200 monitor, 80c seems very excessive. I use my computer near enough everyday for up to 10 hours, and I'm worried about the long-term stress due to such a high temperature.

Is it normal, and if so, safe long-term?

(SMC reset, fans working correctly, no dust in air ducts, etc.)

Answer 1

Well, yes, driving two monitors requires more work from a GPU. But is 80 C normal, long-term-wise? I think not. You can get yourself badly burned at 80 deg, so why would this be good for a computer part, especially over 2 or 3 years? :-/

I remember I had a problem with a Mac Pro years ago. All the RAM slots were occupied, and iStat reported 70+ temperatures in these slots, even though the fans were doing their job. But I had a lot of crashes and kernel panics. Then I thought that such temperatures could not be helping. Then I installed a little helper app that enables you to set the minimum speed for any fan in you system. I just set the fans to 1200 rpms instead of the default 800, and everything began behaving smoothly from that point. Putting my hand to the back of the computer I could really feel the difference in temperature. And the modules' temperature went from 70-80 C to 35-45 C in about 5-10 minutes!!

Of course the fan noises was slightly more annoying, but I was willing to sacrifice a bit of my sanity for a stable computer. :-)

The app was named smcFanControl (http://www.eidac.de/). Works with Lion as of v 2.3. And free. There are of course other apps that would do the same, but this one has worked flawlessly for many years.

I think that Apple is setting it's temperature threshold limits a little too low, all for the sake of silence of operation...

Answer 2

I have the exact same model iMac as you, with two monitors. On my system with one monitor plugged in GPU diode is 66C, GPU heatsink is 58C. With both monitors plugged in the GPU diode was 70C (didn't catch heatsink). My ambient temperature is 17C and the system is basically idle. All fans are running at 1200rpm or lower.

So while I'm not seeing the same temperature jump you are, my temperatures are generally in the same range as yours. Power usage is about the same, too, and I measured a 25W increase plugging in a monitor via DVI. If you really want to see power usage change, try adjusting the brightness of the iMac LCD.

80C on a GPU wouldn't worry me. I was unable to find official operating temperature ranges from AMD, but a quick Google search shows the overclocking nerds often operate up to at least 90C. In general I'd trust Apple's hardware design, they put a lot of thought and effort in to iMac cooling.

Answer 3

I have been using an extra monitor on a 27" iMac (2011). The top right area of the iMac gets very hot (I can't leave my hand on it for too long) and the GPU has been working at around 80C for almost a year now. As soon as I removed the second monitor the GPU temperature dropped under 60C.

Perhaps it is not related, but my power supply started buzzing (sounds like the 50Hz buzz you get from fluorescent lights) and after about of 1 month the computer turned off and did not go back on until it cooled down enough.

This set me back the cost of the PSU (plus some tools) as the iMac is no longer under warranty (I didn't take out AppleCare - but I would expect that something as standard as a PSU would function correctly for longer than a single year).