In a message dated 8/23/01 11:57:31 AM, VW85Westy writes:

<< In a message dated 8/23/01 11:41:46 AM, JKrevnov@AOL.COM writes:

<<  But, first, are you sure the valve plate was sealed
to the body of the pressure cap?  >>

What do you mean by this? >>

Peter,

The check valves of the pressure cap are part of a disk which is inserted
into the pressure cap.  This valve plate, for want of a better name, has a
sealing ring on its circumference.  Tightening the cap to the spigot of the
pressure tank seals the valve plate between the pressure tank and the
expansion tank.  If the valve plate is not forced against the body of the cap
when it is tested, it will not hold pressure nor vacuum.

In my experience, the pressure cap can fail whenever a foreign particle (aka,
caa-caa) becomes lodged on the sealing surface of one of the check valves.
More than once, I have dismantled (carefully!) the innards of the old style
black pressure caps in order to clean the check valves.  Once I found a
thread of paper in there from the cap liner on my well-used coolant refill
jug.  Another time I found a Blue Spruce needle.  Bet you can guess what kind
of trees overhang my drive.

In light of this, and since you had a recent rebuild, perhaps the jobber was
not diligent in cleaning the engine before assembly and there is some swarf
circulating through your cooling system.  A VERY minor piece of leftover
machine work hung up in either pressure cap check valve is all that it would
take to prevent your cooling system from reaching the correct operating
pressure.

Rich