[Joe]

yeh, in the coolant air is suspended when you fill the sytem. That normaly comes out and collects in a few days as the coolant is heated/cooled.

The pump can also hide a good deal of air as well as the water block.

And lastly if you have any Oxidation going on or Bio's living in your coolant that all can also generate gas pockets in the system. But it wont lower the amount of coolant you have much at all, especially to the point that you would need to re-fill the system.