Settings will vary depending upon your environment and system usage patterns. The current settings on our iMac are:
- Lower Temp Threshold : 90F/38C
- Upper Temp Threshold : 160F/82C
- Slowest CPU Fan Speed : 1600
- Slowest HD Fan Speed : 2200
- Slowest DVD Fan Speed : 1000

The current settings on my MacBook Pro 2.33 Core 2 Duo are:
- Lower Temp Threshold : 100F/32C
- Upper Temp Threshold : 180F/71C
- Slowest Left Fan Speed : 1300
- Slowest Right Fan Speed : 1300
- controlled by: CPU for both

With these settings, the HD in our iMac stays below 110F/43.3C (other temps were not an issue and stay similarly low). The temps on my MacBook Pro normally sit with the CPU (diode) sensor at around 120F/48.9C, increase to around 140F/60C when moderately taxed and have seldom exceeded 170F/76.7C. Though I do regularly run tasks that tax both these systems (i.e., keep both processors sitting at 50-70% usage for tens of minutes), I don't do anything that stresses the GPU on either of them.

BTW, if you want to track temperatures, I've found Hardware Monitor to be an excellent application.

Raising the Lower Temp Threshold will control/raise the temperature at which Fan Control begins to increase the fan speeds (based upon the current temperature from the applicable sensor[s]).

Decreasing the Upper Temp Threshold will control/lower the temperature at which Fan Control increases the fan speeds to their maximum (based upon the current temperature from the applicable sensor[s]).

Note that the steeper the slope of the graph's "control" line, the more rapidly fan speeds will be increased as temperatures rise (and vice versa).

While I'm no expert on the subject and/or the components used in any of the Macs ('though I do have an electronics background), my decisions are based upon the following:

- while doing basic browsing, email reading, etc. (i.e. light usage), I wouldn't want any fan to be running at any more than 1/2 of its maximum speed and, ideally, only at about 1/3 of it's maximum speed

- I'd much rather run the fan at a higher speed than suffer high temperatures (the ol' "rule of thumb" in electronics was -- and I'm going way back here! -- for every 10 degrees Celsius rise in temperature [above 20 degrees Celsius], you half the life of the semiconductor)

- my understanding is that hard disk temperatures should be kept below 113F/45C

- I strive to keep chips (CPU, GPU, Airport Card, etc.) always below 158F/70C except in sustained/peak-usage situations and around 131F/55C in moderate use

Hope this helps, a little

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Many thanks for your excellent advice and feedback.
I'll tweak my settings and try to take note of the overall effects.
Thanks again, Richard

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That's great, it works fine BUT should I follow your suggested farenheit profile or the centigrade one. (They aren't the same, you know.)

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Oops! #;-}
[that's a somewhat fuzzy-headed red-faced, sheepish grin]

Sorry, for temperatures I still prefer to think in Fahrenheit ('though, officially, Canada is metric) and, when I was adding the Celsius equivalents, it appears that I put them on the wrong set (i.e., the MacBook's Celsius temps should be on the iMac and vice versa).

Short story, the settings I've arrived at are the Fahrenheit ones.

In reality, you should try some initial settings, watch what happens with your own usage patterns, and adjust as necessary. There's enough flexibility in the settings that it should do a very good job for nearly all usage patterns.



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