Actually, if the Tiger MP you're using is similar enough to the Thunder K7 that preceded it, I wouldn't trust the onboard monitors very much at all.
It seems Tyan did a pretty poor job with the layout of sensors (close counts, apparently), and the hardware monitoring aspects of the board in general--I've basically given up on the ones we run at work.
Essentially what I'm saying, is that the fan is probably either blowing on the thermistor, or is doing a good job of cooling the PCB right next to the thermistor. I found a diagram of the 2462 once upon a time that showed where the thermistors are, but I've lost it. If you want accurate temps, you're going to have to do some soldering...
Check this out if you want to see the details of what I'm talking about. Check out the referenced tickets, as well.