How can this be?

Well, I am trying to cool my computer even more, without spending little or any money. So, I took a spare fan, and cut a hole behind the cpu. I have that fan sucking out all the hot air from behind the mobo and cpu. So, when I boot up and go into the bios to see how exactly my temps are doing, I see that they are around 32 idle. Those are great temps, right? Well, another time I took a fan and put it behind the cpu, I had it blowing on it to cool it down, and the temps were around the same. But when I took it off, the temps went to about 40 idle. So, that fan probably was just blowing cool air on the temp. sensor. So, since this fan is sucking hot air, are these temps legit? Or is the temp. sensor just being cooling down and not the cpu. My mobo is an msi kt333 if that helps any. Thanks.

Try putting blu-tack around the base of your processor socket - where the socket meets the board, not on the pin holes and that should block any air flow over the CPU temp sensor. Then you'll know the reading is at least reliable.