Best way to check for leaks is by pressurizing the system.  Bentley says 16 lbs (the rating of the cap), which you can do with any tire pump that has a gauge.  Go Westy sells one, but it's just a bike tire pump with a tire valve stem screwed into the hose.  The valve stem fits over the nipple on the cap.  You can check the cap by blowing into the nipple, and there should be some resistance and a sound like a trumpet.

Park on a dry smooth surface, or put cardboard under the engine, transmission (if you have an auto), and the radiator so you can see any small leaks. Leave it overnight if you don't see anything immediately.  I found both heads dripping slightly, which was fixed (at least temporarily) by the addition of two bottles of Subaru head gasket additive. 

If your system is pressurizing from a leaking sealing ring at the cylinder/head interface, it's rebuild time. But that usually leads to the overflow tank spewing coolant. :-(

Stuart

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of Eric Caron
Sent: Friday, June 17, 2016 1:31 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Coolant mystery

OK folks,

        Be gentle here as  coolant questions way to often end up with very scary responses.

I’ve noticed that even a few days after a bus trip the van has air in the expansion tank.  usually the tank is about 3 fourths full.  If I turn the blue cap I hear bubbles and sound of pressure.  today a sighted friend told me that when I did this the expansion tank filled up with coolant.  Interestingly the level of the over flow tank never seams to change.

The van was recently checked out at a VW shop and he was suspicious that a tiny seep of coolant might be coming from one head but it was so slight he could not be sure.

So, my van seems to build up pressure when running and holds it for several days.  Once released the expansion tank fills but level of overflow seems consistent.

Is this normal or a sign of something needing attention.

temp indicator is consistently just below the led.

Eric Caron 
85 GL Auto Westfalia