Followup to CPU temperature and PSU fan

On March 11, 2008 I mentioned that my power supply is mounted such that its fan draws air above the CPU heat sink and exhausts it to cool the CPU. The computer case also has the option of mounting the power supply such that it draws air from the top of the case so the power supply can breathe cooler air from outside the case. I wondered what would be the difference between the two configurations for my CPU temperature. It turned out to be a huge difference.

The original configuration where the PSU help cool the CPU, I call configuration 1. The second configuration where the PSU only cools itself, is configuration 2.

Config 1
@Idle: 36C
@Load: 50C

Config 2
@Idle: 60C

During testing in configuration 2, I let the computer idle and waited for the temperature to settle. It kept going up and once it hit 60, the BIOS alarm starts to go off because that's the current setting. I thought this is too high to be acceptable and didn't proceed to test the temperature at loading condition.

From this comparison, it is obvious that the CPU heat sink needs a good amount of air flow to cool efficiently. Since it doesn't have its own fan, it relies on other fans in the system to move air through its fins. There are two small exhaust fans at one side of the heat sink, but I think the vertical air movement is much more important than horizontal ones in cooling the heat sink.