A shop should have the equipment to test the cap and the complete system
including the cap. If the plumbing on the conversion is correct there should
be no need to go back and bleed the system after any period of time unless
there are leaks either internal or external or something is causing coolant
to get blown out. Another possibility is that the system is not plumbed
properly for it to self-bleed/purge. The gauge only reads the temperature of
the coolant flowing past the sensor. If there are blockages or vapor pockets
you can have steam build up and if bad enough the cap may open but not have
enough capacity to deal with the problem so hose failures are the next
hopeful step. Better to lose a hose then to blow the sides of a heater core
or radiator.

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Doug Alcock
Sent: Sunday, July 28, 2013 7:55 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Checking pressure cap function???

Hi gang -- I've been blowing hoses on the coolant system ---- is there any
way to check if the pressure cap is functioning correctly. My understanding
is that the pressure cap should be venting at 15 psi. It is a new pressure
cap. I have an 84 Vanagon that has a I4 (1.8 from a VW Jetta) in the back.
The Vanagon cooling system remains the same. New waterpump (new engine
actually), new thermostat and the rad was replaced about 8 years ago. I've
blown 2 hoses since the new engine. I'm pretty sure the system has been bled
correctly -- I've been putting coolant into the system from a tiny hose that
goes into the front bleeder (highest point in the system) and leaving the
highest points in the engine open until they fill -- closing them and then
continuing to fill until done. Then I bleed from the front over a couple of
days. The temp needle stays where it should, the fan goes on when it should
and everything seemed fine until the other day when I blew the top hose on
the engine -- which both my I and the machanic who had done the engine
agreed looked and felt fine. So I'm thinking the coolant system is creating
too much pressure. Hence my request for a way to check if the cap is working
as advertised. Grateful for any other thoughts from the fount of wisdom that
is this list.

Thanks,
Doug

--
http://www.dougalcock.com