Nelson's log

Mac fan control

My ~3.5 year old iMac is making noise. Just a small noise, but it’s high pitched and annoying. Something mechanic, presumably a fan bearing. So I started trying to isolate the source of noise. It isn’t the internal spinning drive, you can turn it off by unmounting all the volumes. I’m not using the optical drive. So maybe a fan?

The tool to test a Mac’s fans is smcFanControl, a simple tool to read the temperature and fan speed settings and alter fan speed. When you run it it requires root access, then goes into your menubar. You can set the minimum fan speed for each fan separately. It works pretty well. I used it to run each fan at full speed and crikey, my Mac sounds like a vacuum cleaner. Never heard those fans run before! Didn’t really notice a change in the sound but it’s hard to be sure. Maybe my optical drive fan is to blame. Unfortunately you can’t set turn the fans off entirely; the apps docs say this is possible but not enabled for safety. A quick search didn’t turn up any easy hacks, either.

On a side note, apparently there’s no good CPU/GPU/Memory burn-in tool for Macs. At least not a free one. The #1 suggestion from Google searches is “run yes > /dev/null”. Which, well, that works a tiny bit but it’s not even exercising the whole core of a single CPU, much less the whole system. There’s a bunch of good tools that run under Windows, too bad no one’s bothered to port one. The core load generator doesn’t need to change (much?) but the GUI is a problem.