that filler neck isnt a big enough "reservoir" to properly bleed out the air from the system. if you fill it to the top when its cold and go do a few pulls and check it, it will have pissed some out, then if you let it cool all the way back off and check it, more than likely the coolant level will be lower than the filler neck letting air back into the system

 

This is true. If you fill it when it is cold, and pull a few times, it will definitely **** out.

Also true that if you let it cool after that, the coolant will be lower than the neck.

You want to fill it when it is hot. That is why the filler says "Hot Level" on it. You should not fill it when cold.

 

either way, every time it cools it getting/keeping a bit of air in the system

 

wow, you may want to look that over and then mabe edit your post after you find out your results of examing filler neck setup then ask yourself does it realy bleed itself.