Well, I finally did it. I opened up my iMac and found out why the system was running so hot and loud.
FYI for four of the last six years my Early 2008 iMac has progressively been running hotter and louder. In the last two years it had become crazy loud. The weird thing is that I would boot in, not open any app and within 15-20mins the CPU fan would be roaring at 3600RPM.
Last weekend I decided to do it.
After opening it up and removing the display unit I found a fine layer of dust sprinkled over the components and EMI shielding. An acceptable amount. The HDD and ODD fans were almost spotless but, as I suspected, there was a proper buildup of dust on the CPU fan. This is where it gets interesting.
After removing the left speaker and CPU fan (the latter is really fiddly) I was shocked to discover that half of the heatsinks was blocked with dust. This meant only half of the air successfully passing through the heatsinks was cooling it and the PSU. It completely explained why the left side of the Mac was so hot to touch and why the temperature sensor readings for the CPU and GPU were in the high 60s/low 70sºC and high 80s/low 90sºC for the PSU.
It was dust all this bloody time! The odd thing is that I actually keep a clean desk. I guess that's what six years of dust build up does.
From there I removed the right speaker and logic board, took the components and iMac shell outside and gently blew compressed air onto them. Next I wiped everything with an anti-static cloth, put the Mac back together again, plugged in the power cord and switched on the Mac. BONG! It's alive!
For the next hour I performed a Apple Hardware Test (everything A-Okay) and stress-tested the Mac with CPU-intensive apps and GPU-intensive games. Other than from playing CS:GO when the CPU fan hit 1400RPM (which is unbelievable) the CPU fan did not exceed its base speed of 1200RPM. Amazingly the temperatures on some components are about a third to half of what they were before.
It's nearly been a week now and it's still running whisper quiet. Overall I'm very satisfied with the results and pleased with myself for undertaking this task.
The next and final task is much more stressful.
The LCD exhibits shadows on parts of the screen and I want to get rid of that, therefore I will have to disassemble the LCD unit and wipe away the dust that has somehow made its way between the actual LCD and the backlight and causes these shadows.