I have an overheating issue on my netbook (ASUS EeePC 1015PW), which I'm trying to troubleshoot. Using lm-sensors while overheating gave me this output :

acpitz-virtual-0
Adapter: Virtual device
temp1:        +86.0°C  (crit = +100.0°C)   

eeepc-isa-0000
Adapter: ISA adapter
fan1:        4089 RPM 

coretemp-isa-0000
Adapter: ISA adapter
Core 0:       +82.0°C  (crit = +100.0°C)
Core 1:       +80.0°C  (crit = +100.0°C)

But I can't hear the fan. So I enabled manual pwm controling and set the fan to full speed, and after a few minutes I got this output :

acpitz-virtual-0
Adapter: Virtual device
temp1:        +65.0°C  (crit = +100.0°C)

eeepc-isa-0000
Adapter: ISA adapter
fan1:        4016 RPM

coretemp-isa-0000
Adapter: ISA adapter
Core 0:       +62.0°C  (crit = +100.0°C)
Core 1:       +58.0°C  (crit = +100.0°C)

And this time I could hear the fan spinning. So there's quite obviously an issue with either fan control or fan monitoring. Hence the question : what kind of physical information does the fan sensor really report?

Thank you

PS. I should have added that the computer is a small, hard-to-disassemble netbook, so I can't and don't want to try experiments like "block the fan and see what the sensor reports".