iBook G4 - Fans not working?

Hi all.
A little advice please.

I have bought a used G4 ibook from ebay - with a logic board problem, which I have fixed in the main, but, having not owned a laptop before, I am unsure as to whether the cooling fans should be running all of the time, or only when it reaches a certain temperature?
It seems to get very hot, and I have not heard the fans come on, nor can I fell any air from the vents.
It will run fine for 2 hours or so, then switches itself off. I don't think that the logic board is to blame for that, so wondered if it was a temperature issue.
Any advice appreciated. Kev.

I own a 1.33ghz G4 iBook... the fans only come on when I'm doing something intensive like photoshop or Garage Band... mostly it is silent for surfing/email etc... it does get very warm by the left 'palm rest' (where the hard disc is - hence the little vents there)...

Download 'Temperature Monitor'... its free... gives the temp. of various parts of your iBook... worth a download...

Thankyou. I'll have a look for that shortly. The "hot spot" is in the same place, so I guess it's a normal thing.
Maybe the logic board is still playing about a bit then. Out with the screwdriver!