Yes it is a bleeder as Ken noted. Be careful with it. Overtightened they
like to have the head break off and the coolant will then just fill the van.
Since it is never needed consider replacing it with an 8mm fine thread bolt.

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Dennis Jowell
Sent: Tuesday, July 21, 2015 6:40 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Rear heater core question

Does anyone know what that small white cap on the rear heater core does?
1988 Westy GL.
I am working on changing coolant lines. I think it may be a breather for the
heat core. My Bentley has no information .

Dennis Jowell
Scotch Hollow Farm
Newbury, Vermont