Since I got my new Lenovo ThinkPad X61, I have discovered that the CPU fan is behaving rather differently than the one I have in my IBM ThinkPad X31. That is the fan makes a lot more noise when idle on the X61.

For the record. I’m running Ubunty Hardy (8.04) on the X61 and Ubuntu Gutsy (7.04) on the X31. Both 32-bit systems.

The first thing I did was checking Launchpad.net for any known bugs. I found bug 224876 to be promising, it’s titled “Hardy does not control the CPU fan properly.”
After reading this thread I ran the tests described myself, which gave these results.

Machine temperature and fan speed when idle (X61):

$ cat /proc/acpi/thermal_zone/THM0/temperature
temperature: 41 C
$ cat /proc/acpi/thermal_zone/THM1/temperature
temperature: 42 C
$ cat /proc/acpi/ibm/fan
status: enabled
speed: 3207
level: auto


After 5 minutes of “yes | sha512sum” (X61):

$ cat /proc/acpi/thermal_zone/THM0/temperature
temperature: 76 C
$ cat /proc/acpi/thermal_zone/THM1/temperature
temperature: 78 C
$ cat /proc/acpi/ibm/fan
status: enabled
speed: 3242
level: auto


As you can see there is as good as no change in the fan speed.
However; doing the same check on my older, one core, IBM ThinkPad X31.
I get this results:

Machine temperature and fan speed when idle (X31):


$ cat /proc/acpi/thermal_zone/THM0/temperature
temperature: 44 C
$ cat /proc/acpi/ibm/fan
status: enabled
speed: 0
level: auto


Actually, the fan doesn’t start until the temperature reach 68 degrees Celsius. Then it will speeds up to around ~3500 rpm, thus keeping the processor at around 70 degrees Celsius during “yes | sha512sum”.

My question is: Why does the fan constantly run on the X61? Is it really necessary to keep the processor cool? I must say I prefer the silence of the X31 when I’m just browsing the web.

Karl Trygve has suggested that this is a result of a new design team and BIOS which is more restrictive than the one found on the X31.