I have NEVER been able to blow or suck through any of
the 4 or 5 caps that I have  (and I have two different types
of caps, Euro and American, I think).  But both caps hold
the 13 to 17 psi pressure (as Rico says) till I'm stuck in
traffic on a HOT day with a HOT engine, then the caps let
go and the level in the 2nd (fill) tank begins to rise and
then fall again as I begin to drive and the coolant cools
off.  I know this as I have driven with the engine cover off
with my wife back there watching the damn thing.
M2CW,  Malcolm

On 23 Aug 2001, at 11:39, Rico Sapolich wrote:

> In a message dated 8/23/01 11:14:03 AM, VW85Westy writes:
>
> << Are you absolutely sure about this?  I just bought a new
> one, and it let me suck air through it easily. >>
>
> Peter,
>
> Unlike others, if I were not certain, I would not have said
> it.  I guess we have to define "easily".  But, first, are
> you sure the valve plate was sealed to the body of the
> pressure cap?  If not, blowing and sucking on the cap will
> prove nothing.  The cap should relieve system pressure @
> 13-17 psi positive pressure and 0.3-1.45 psi negative
> pressure.
>
> Rich