Now that the Laptop internals are dust-free the core temperature droped about 5ºC~10ºC, which is A LOT. As i suspected to be because of dust inside.
On the cleaning process: I’ve completly cleaned the fan + heatsink. I’ve placed a vacum cleaner in reverse-flux near the heatsink and another small vacum in the other end of the sink (where the cooler is) and with this “trick” I’ve cleaned the majority of the dust inside.
Measuring CPU temperature in Linux:
1) lmSensors – is probably the best acknowledged one. (guides here and here)
(you can then set an applet for gnome called sensors, that will show the temperatures of your cores.)
2) ACPI Lib – is a possibility
3) Ksim – is another one
p.s.: For Windows users I recommend CoreTemp.