Yes, the caps go bad. The pressure relief will fail, the gasket will fail.
Pressure testing of the cap needs to be done on regular bases. Operation
with a bad cap will eventually cause problems including poor internal engine
cooling. The coolant needs to be pressurized to maintain contact with the
internal surfaces. The cap should really be replaced after any cooling
system failure. They are cheap enough to carry a spare. 

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Todd Guttman
Sent: Wednesday, September 02, 2009 5:22 PM
To: vanagon@GERRY.VANAGON.COM
Subject: leaking coolant - reservoir cap failure?

Group,  

A simple but hopefully not-too-stupid question.� After years of fairly
trouble-free duty by our 85 Westy's cooling system (except for the p-i-t-a
annual drain, refill, point-to-the-sky, top-off and repeat process), it is
leaking coolant - specifically around the cap of the coolant reservoir.� 

The cap is on tight.  Also, coolant placed in the overflow tank when the
engine is cold appears to be getting sucked back up to the reservoir tank.
The overflow tank has been empty, however, when the leak occurs - after the
engine temperature has gone past the mid-line of the temperature gauge from
extended idling. 

The question: do the reservoir caps simply go bad and the two-way valve in
the cap stops directing coolant to the overflow tank behind the license
plate?�  

All comments, guesses and opinions are greatly appreciated! 

Todd
Columbus, Ohio
85 Westy (Rivendel)