The most common real cause of combustion gasses getting into the coolant is
really loose heads. Testing at idle and low speeds often will not reveal the
problem as the engine has to be really loaded to lift the heads and let the
gasses out.  Recently I had a problem with a head that was cracked in the
exhaust port. This was tough as the only symptom was coolant in the exhaust
but since the crack was after the exhaust valve did not show in a leak down
or cylinder pressure test.  I pressurized the exhaust system and the problem
became apparent real fast.

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Travis Newhouse
Sent: Sunday, September 25, 2011 1:09 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: 85-H20 loss of coolant mystery

I got a Block Tester at Auto Zone today - a little tube that holds blue
fluid that will turn yellow when exposed to exhaust gas.

I opened the expansion cap, started the motor, placed the block tester's
rubber cone sealed against the opening of the expansion tank, and began
pulling air through the little tube with the bulb.  I tried for several
minutes.  Fluid stayed blue.

I checked on the temperature gauge, engine still coming up to temp.  I tried
again to pull air from the expansion tank through the blue fluid in the
little tube.  Fluid stayed blue.

Engine is starting to warm up now.  I noticed that the level in the
expansion tank has risen a little.  I try again with the block tester.
 Fluid stays blue.  I notice the level rising in the expansion tank, and go
to shut off the engine.  Too late.  Thermostat must have opened.  The
expansion tank overflowed and steam billowed out of the back.

Doubting the block tester, I replaced the expansion cap and restarted the
engine.  I held the block tester near the tailpipe and pull air through it.
Fluid turns yellow.

I'm feeling pretty good that exhaust gas may not be in my cooling system,
and the head gaskets are probably still doing their job.

Tomorrow I'm going to go over the engine and cooling hoses once again and
look for signs of leaks that could be allowing air into the cooling system.
Unfortunately, I couldn't find a pressure tester that fits the threads on
the expansion tank to help me out.  Does anyone know if any chain auto parts
stores or car dealerships sell an adaptor that fits?  Do any other makes
share the same threads?

Thanks to all who have offered their help.
Travis Newhouse
Encintas, CA