Hello everyone, i have an iMac 20" (8,1), 2.66 GHz C2D, 4GB RAM and an ATI HD 2600 Pro graphics card. Whenever I run Snow Leopard the temperatures for the GPU are really high. The GPU Diode temperature is always around 70°C and after some time the CPU fan speed starts to increase to cope with the heat. As soon as I return to Leopard that temperature drops to around 60°C and the fan speed goes back to 1200 rpm (see attachment for screenshots of iStat Pro in Leopard and Snow Leopard). Here are some things I already tried/ruled out: PRAM/SMC Reset: I did that countless times but did not help. Bad installation/hard drive: I reinstalled Snow Leopard about 10 times using my internal drive, external drive and even using my MacBook to do the installation and then booting from it on my iMac. I also booted from my iMac hard drive with my Macbook using Target Disk Mode. It runs fine on the Macbook but on the iMac the temperature is still too high. I also reformatted the whole hard drive to force a rebuild of the EFI partiton. Background processes/Spotlight: Nothing shows up in Activity Monitor or top in Terminal. Spotlight had also already finished indexing. Bad RAM: I replaced my 4GB 3rd party RAM with the 2GB the iMac came with, no change. Hardware conficts: I detached everthing except for the keyboard and mouse. I even did an installation that way. Replace iStat Pro: Since iStat Pro was the only software that I installed after a fresh install, I used different applications to monitor the temperatures and make sure iStat isn't actually the culprit. Temperatures were still the same. Log files: Nothing suspicious. Right now, I am out of ideas. Leopard runs fine on my iMac and even Snow Leopard works great except for this stupid temperature bug. I already called Apple hoping this to be a known issue but instead they told me they never heard of it before. They had me run a diagnostic program and send them the results but told me it will take a week to examine the data. I suspect that a bug in the ATI driver prevents the GPU from entering power saving mode. I attached my iMac to a power monitoring device and it uses around 10W more in Snow Leopard than in Leopard. But why does it happen to only a very few iMacs? I only found reports of 2-3 people having the same issue. Does anyone of you experience the same temperature increase or am I (nearly) the only one with this behavoir?