I could never get proper temperatures on my Dell Studio 1558. lm-sensors and acpi give wrong readings. The output of sensors is,

$ sensors
acpitz-virtual-0
Adapter: Virtual device
temp1:       +26.8°C  (crit = +100.0°C)                  
temp2:        +0.0°C  (crit = +100.0°C)

acpi -V gives me,

$ acpi -V
Battery 0: Full, 100%
Battery 0: design capacity 414 mAh, last full capacity 369 mAh = 89%
Adapter 0: on-line
Thermal 0: ok, 0.0 degrees C
Thermal 0: trip point 0 switches to mode critical at temperature 100.0 degrees C
Thermal 0: trip point 1 switches to mode passive at temperature 95.0 degrees C
Thermal 0: trip point 2 switches to mode active at temperature 71.0 degrees C
Thermal 0: trip point 3 switches to mode active at temperature 55.0 degrees C
Thermal 1: ok, 26.8 degrees C
Thermal 1: trip point 0 switches to mode critical at temperature 100.0 degrees C
Thermal 1: trip point 1 switches to mode active at temperature 71.0 degrees C
Thermal 1: trip point 2 switches to mode active at temperature 55.0 degrees C
Cooling 0: LCD 0 of 15
Cooling 1: Processor 0 of 10
Cooling 2: Processor 0 of 10
Cooling 3: Processor 0 of 10
Cooling 4: Processor 0 of 10
Cooling 5: Fan 0 of 1
Cooling 6: Fan 0 of 1

I suspect even hddtemp gives bogus readings as its always at 46

$ sudo hddtemp /dev/sda
/dev/sda: ST9500420AS: 46°C

I have gone through some bug reports and some used to have the same problem after resuming from suspend. But I always have this problem.

I had updated to the latest BIOS from Windows a couple of weeks ago, will updating from Ubuntu change anything?

CORRECTION: hddtemp's readings do change. Its now at 45.