So I pulled the cover off, blasted the dust. Knowing that while the cover is off the heatsink is just sitting on top of the GPU not held down by anything but the thermal grease, I decided I might as well swap the nasty white grease out with some fresh new arctic silver.
Now the GPU reports 46-47C idle in windows instead of 50C, but the temps in 3d still show as high as 91C, the core shutdown temp in the drivers is 140C. So I wonder, is this thing really hot enough to run a coffeemaker or is the driver just reporting it wrong? The card does get too hot to touch while running but stability has never been a problem and the card overclocks well clear up to 500 MHz core.
Under the leadtek shell the card is a refrence board FX 5900 ultra with 2.2 NS BGA ram. Maybe I should get a waterblock for it.
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http://www.indianheadtel.net/~dutennj/temps.gif