I have to agree with relaxx and sudeki regarding inaccurate temperature readings on the slims.
I had my slim JTagged a few weeks ago by a local reputable technician, and he set things up so that it boots into FSD 2.2.725. Temperature readings when using "Auto" mode were quite high; CPU temps were in the 79-81 degree range, with the GPU temp ~4 degrees lower, memory ~8 degrees lower, and the case hovering around 49-50 degrees. XexMenu (which was also installed) showed similar readings.
During these first few weeks, I've had the fan set at 65% speed, which lowered the CPU to ~57 degrees. However, I'm not a "fan" of the noise, as I've been used to a whisper-quiet XBox for the past 18 months.
At any rate, I've just set the fan back on "auto" (i.e. whisper-quiet mode), and after 45 mins the air coming out of the console feels no hotter than from before my slim was JTagged. The console case itself isn't hot to the touch at all. This leads me to believe that all is functioning normally, with no need for me to ramp up the fan's speed.
This is good news, as during the past couple of weeks I've been looking into options to either replace the fan with a quieter one, or have the NAND flashed with lower temperature threshold settings. Since I had my XBox JTagged by someone else, I had no desire to try implementing either of these options myself.
At any rate, I'll try running things in "auto" mode for the next few days / weeks to be sure that all remains well (i.e. no red dot of temporary death). I just wish I found this thread sooner... so many XBox threads to read through, but most of them aren't very useful because they mainly deal with the old XBox consoles, or deal with older versions of FSD that didn't support fan control on slims.
Edited by Visor4, 06 February 2012 - 11:33 PM.