Ben,

No, when I replaced the expansion tank I just put the new one in, filled
it with new coolant and bled the system.  It was a few days later when I
was replacing the .9 bar oil pressure switch when I siphoned off the
coolant from the expansion tank so I could remove it from the exhaust
shield (somewhere I read that shifting the shield was necessary to
remove and replace the oil pressure switch - wrong!) when I noticed some
black residue in the bottom of the tank.  I didn't think much of it at
the time, but this was the remnants of the T-stat seal that had broken
away.

No idea why the seal broke away, here is a picture:
http://www3.telus.net/eunrau/Tstat.JPG

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf
Of The corruptor
Sent: Friday, April 09, 2004 6:46 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Rad Fan isn't working properly

Clogged Radiator will block the coolant flow mostly at highway speed,
more
air resistance, more heat, less flow, more pressure.

He said that the system was fine before, he did something wrong in
between.

What am curious to know, did you play with the thermostat wile bleeding
or
changing the exp tank?

Let us know why the thermostat had a broken seal, your answer could help
others.

Cheers
Ben
http://www.benplace.com