How fast should a hot laptop's fan spin?

Question

I am having some problems with my T420 Lenovo laptop overheating. The fan is working, in that I feel air being blown and can hear it when I put my ear near the heat sink fins. I have noticed however, that I no longer hear the fan speed increase noticeably, even when the laptop is under load.

The laptop is running a fully patched OpenSUSE 13.2 Linux distribution.

This is the output of sensors when the system is not under load:

acpitz-virtual-0 Adapter: Virtual device  
temp1: +53.0°C  (crit = +98.0°C)

thinkpad-isa-0000 Adapter: ISA adapter fan1:  
     3575 RPM

coretemp-isa-0000 Adapter: ISA adapter  
Physical id 0:  +53.0°C  (high = +86.0°C, crit = +100.0°C)  
Core 0:         +53.0°C  (high = +86.0°C, crit = +100.0°C)  
Core 1:         +48.0°C  (high = +86.0°C, crit = +100.0°C)

And output when under load:

acpitz-virtual-0 Adapter: Virtual device  
temp1:        +90.0°C  (crit = +98.0°C)

thinkpad-isa-0000 Adapter: ISA adapter fan1:  
     3868 RPM

coretemp-isa-0000 Adapter: ISA adapter  
Physical id 0:  +93.0°C  (high = +86.0°C, crit = +100.0°C)  
Core 0:         +92.0°C  (high = +86.0°C, crit = +100.0°C)  
Core 1:         +93.0°C  (high = +86.0°C, crit = +100.0°C)

According to sensors, the fan speed increases ~8% when nearing critical temperatures.

I think the fan is set to auto speed.

cat /proc/acpi/ibm/fan 
status:         enabled
speed:          3591
level:          auto

How fast should the fan be spinning when under load? I think it should be faster because I can remember the fan noise being easily audible at times months ago.

And if there is a problem, how can I troubleshoot the OS fan control?

Answer 1

You should investigate why the processor is getting so hot in the first place... almost certainly going to be dry thermal paste or a clogged heatsink/vent.

You should fix this problem first as it didn't do it when you first bought the laptop, right?

Answer 2

My T420 has also recently started having over-heating issues. I opened it up and blew out all the dust but it didn't help. From other reading I've done, there seems to be a consensus that the cpu (and perhaps gpu) thermal paste likely needs replacing.

However, that being said, your fan is spinning considerably slower than mine when my CPU heats up like that. I was just seeing the numbers 4460 and 4477 rpm when my cpu temps were in the mid 90's C. I'm also running linux.

This is with an external monitor attached, and unplugging from that seems to reduce the overheating a LOT. I'm not sure if that could suggest a non-hardware cause or just the integrated intel graphics generating too much heat for the failing thermal paste.

Answer 3

You may look for some third party software like Thinkpad Fan Control which is working on my X220 to manually control the fan speed on your computer. If you are able to set it on max speed with the software, that means the hardware is no problem. I am not familiar with Linux so I can't tell if there is some fan speed configuration file installed in OpenSUSE is throttling the fan speed.