Coretemp seems to be off quite a bit

[Kirk Strauser]

I have a Gigabyte motherboard with an Intel ICH-9 chipset, and a  
3.0GHz Core 2 Duo (E8400).  The coretemp sysctls seem to always show  
50C as the baseline temperature:

$ sysctl dev.cpu | grep temp
dev.cpu.0.temperature: 50
dev.cpu.1.temperature: 50

This is with a big PSU fan, a good CPU fan, a clean heatsink, and two  
case fans aimed the right direction (front fan pulling cool air in,  
rear fan pushing warm air out).  If I reboot and go into the BIOS, I  
get numbers around 42-43C.  I know it's kind of hard to compare  
directly, but the coretemp numbers are from a totally idle system with  
powerd scaling it back to 373MHz, so it should be as cool as when  
sitting idle in the BIOS screens.  When I work the system hard, like  
running "make -j4 buildworld", I see temperatures up around 63-64C,  
and I'm almost positive that's not right.

Any ideas why coretemp and the BIOS would show such different numbers?
-- 
Kirk Strauser