I have another post on this, but thought it was worth posting here. I will paste the text from my other thread here:
I bought a used GPU heatsink off ebay for $5 and bought some Arctic Silver thermal paste from Amazon for $10.
I replaced the heatsink and used new thermal paste, and after 90 minutes of having my son play Minecraft on it, the fans arent spinning fast and the GPU temps are staying around the 120 (f) mark.
Before, after about 5-10 mins of the computer sitting idle, the temps would have skyrocketed.
I hope I am not speaking too soon, but so far, this looks promising. I dont know if the problem was a bad sensor, heatsink or thermal paste, but for a $15 repair, I dont care which was the problem. I might have just gotten another year of life out of this thing.
Currently Being ModeratedMar 25, 2013 7:24 AM (in response to BTfromNC)
Not so good news:
It's the operating system (10.8.3 in my case) that causes the spike in GPU temps.
Other users report that downgrading the operating system solves the problem.
In Bootcamp with Windows 7 the GPU temperature is around 60º C, while in OS X 10.8.3 everything related to the GPU is at least 20º C hotter. The Graphics Processor's load in 10.8.3 on my iMac is around 15% on average.