I've been having the same problems with my Imac 2006 with the NVIDIA GeForce 7300 GT card. I installed SMC Fan Control and it helped, I cleaned the fans 6 months ago.
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Anyway I took the computer apart again and cleaned it throughly. When I took apart the fan on the left side, unsnapping the duct cover, there was a large amount of dust on the radiator fins of the graphics cooling heat sink. I estimate it was plugged about to 50%. I vacuumed it out and cleaned the fans, it seems to run cooler now as more air flow gets across the heat sink....See the picture I found off the net and put a red arrow at the location to clean.
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Anyway I took the computer apart again and cleaned it throughly. When I took apart the fan on the left side, unsnapping the duct cover, there was a large amount of dust on the radiator fins of the graphics cooling heat sink. I estimate it was plugged about to 50%. I vacuumed it out and cleaned the fans, it seems to run cooler now as more air flow gets across the heat sink....
There was also a bit of dust on the air intake on the bottom of the computer.
I've been having the same problems with my Imac 2006 with the NVIDIA GeForce 7300 GT card. I installed SMC Fan Control and it helped, I cleaned the fans 6 months ago.
Anyway I took the computer apart again and cleaned it throughly. When I took apart the fan on the left side, unsnapping the duct cover, there was a large amount of dust on the radiator fins of the graphics cooling heat sink. I estimate it was plugged about to 50%. I vacuumed it out and cleaned the fans, it seems to run cooler now as more air flow gets across the heat sink....See the picture I found off the net and put a red arrow at the location to clean.
There was also a bit of dust on the air intake on the bottom of the computer.
It's worth a try.
Ed