Intel CPU fans -- The answer

I did some experimenting. On a 3-wire CPU fan, yellow is power (+12V or less, down to about 8 V for slow speed), black is ground, and green is sense (open collector to ground, square wave, one cycle per revolution, so 90 Hz =

5400 rpm = full speed).

The supply voltage is adjusted by the motherboard on the basis of the measured CPU temperature, which should be between 40 and 50 C.

If the temperature stays below 40 C, you can experiment with putting 1N4001s in series with the yellow lead so that the default speed will be lower. People are marketing "quiet fan cables" that do this.

Quality of the heat sink grease between the CPU and the heat sink is critical. I now know from personal experience that the silver-powder grease sold in computer stores is MUCH more conductive than ordinary white heat-sink grease.

No kidding!

I once removed the CPU fan from my 2.7ghz Celeron in order to add a second hard drive. Afterwards, my computer kept locking up. If I left the computer on overnight, guaranteed it would lock up.

Finally traced it to inadequate heat paste. Bought some Arctic Silver, no more hangups! I could even overclock it to 3 ghz, no problem. That $10 for Arctic Silver was really worth it.

I did add an extra case fan, though, just to be safe. (Another $10.)

Then I realized I don't demand much from my system anymore (mostly now use it just for web surfing) so I returned the CPU settings to defaults (no more overclocking). System runs a bit cooler now (air blowing out of the case isn't as hot).

Michael D.