Chosen Solution
The CPU/Video fan runs slow at startup, and gets ridiculously fast and loud after a few minutes. I disassembled the computer to remove 3~4 years of dust on the heat pipe fins, but the problem remains. It is the nVidia logic board GPU that is running at 160 deg F. It has the CPU/GPU fan running at a full 3600 RPM. Is this in spec or am I going to need to try to re-seat the heat pipes to get a better thermal connection?
did you replace the thermal paste on the cpu/gpu? i had a few macbooks with heat problems, the paste was hard and almost useless - in other cases, there was way too much of that stuff on the chip’s (original apple!).
replacing it is a must!!
Try downloading a demo of iStat menubar. Then you will get a good look into the CPU processes and temperatures in your iMac. heres the program
You could also try Activity Monitor, which is included with OS X.
