> If You have air in the expansion tank, the tank cap doesn't work.
> If the water volume extends, the air on the top of the expansion
> tank will be pressed through the cap and the small hose into the
> refill tank. While cooling down, water is sucked in reverse
> direction. In this way, the expansion tank must always be total filled.
> If not, cap must be replaced and/or the cooling system has a
> leak, where air is sucked while cooling down.
>
> I had these problems to and VW wasn't able to fix it. The
> description of the tank caps function is wrong in Bentley.

But I don't have air in my tank now.  It's all been replaced with coolant.
There was less air after each filling/driving session.  Now my cooling
system is working fine.

Bryan