The problems occurs in Windows and Linux, therefore I updated the BIOS from version 1.16 to 1.20. Now the problem is over, the fan works again like it should. I will monitor the temperatures the next few, just to be sure.
Last week I bought myself a Lenovo Thinkpad L512.
The same day I installed Gentoo Linux and started tweaking acpi.
After a fews days I got the machine to run very cool, it uses around 9 Watts idle.
However today (after playing some Scorcher
in Dosbox, first time after switching dosbox option output=surface to output=opengl) I noticed that the videocard / processor became really hot. So i immediately did 'rmmod thinkpad_acpi' and 'modprobe thinkpad_acpi fan_control=1', and started the fan on top speed.
After a reboot I started the game again (however now with output=surface in the dosbox, instead of output=opengl). Still the fan didn't start automatic.
I'm sure the was autocontrolled before. I have no idea what the problem might be.
If you need more info, I can post it here.
I hope you can help me, as I think this is a very big problem.