Hi guys,
This morning a friend woke me up to check his car.  His water was overflowing from the overflow tank.  When it cooled down, all the water has been sucked back to the engine and still some were missing.  I proceeded to bleed the system but I knew something must be amiss.  In the process I noticed that bubbles were constantly coming out of the top hose of the pressure tank and I traced it back to the right cylinder head direction.  
The question is; what is this phenomenon and what is the remedy?
Zoltan
My guess is, that the top O ring of one of the cylinders of the right side head is leaking through because the head is not flush with the cylinder and now it is probably already created a passage that won't be closing with the retightening of the head.  The car is 13 years old.  Yes, it is a '91 model which sound like 2005 to some of us, but it is an older car now and all the syntetic gaskets have aged in it.  In this case the engine would need a whole gasket change in my opinion.