On the AMD stock cooling fan (I have an Athlon 64 4800 *2), should the fan blow air down over the heatsink, or extract hot air from the heatsink and blow upwards? I have a Centurion 5 case which has a side duct that is above the CPU fan, and I'm considering placing a fan there to help cooling. The air through the duct appears to be flowing out of the case, which would imply that the CPU fan is blowing hot air upwards and away from the CPU, and so an extraction fan would be the type to fit. But reading about CPU cooling, it appears that the CPU fan air actually flows the other way.Thanks, Bruce.

Hey Bruce,CPU fan always blows onto the heatsink, (downwards).Follow this link for a quick 101, about creating the best cooling setup: http://www.extremetech.com/article2/0,1697,1835927,00.asp

Thanks again, Davis. Interesting stuff!Bruce.