It is possible for an external coolant leak to allow air to enter the
system. When the system cools down, it will pull a vacuum as the coolant
contracts. This is how coolant is returned to the system from the
recovery tank. A leak of the correct size and location will allow this.
The ones I have come across are the hose connections for the large
coolant pipes and a leaky from heater core. Also, you need to make sure
the pressure cap is functioning properly, both the pressure relief and
return valve. A sticking or clogged return will cause the system to try
to suck in someplace other than the recovery bottle.

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf
Of Doug F
Sent: Saturday, April 01, 2006 9:26 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Air Getting into Cooling system

How?
A compression test will not reveal a tiny leak which is plenty to pump
up
the cooling system with air.
I had this exact same problem with my 85 sunroof GL.
Got progressively worse because air in the system continues to overheat
stuff. Eventually it got so bad I had to admit it was the heads.

The cooling system runs pressurized so any leaks will not allow air to
enter
but instead create a leak of antifreeze on the ground.

Betcha a nickel its the heads.

Doug

Doug

----- Original Message -----
From: "John Connolly, Aircooled.Net" <john@AIRCOOLED.NET>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Saturday, April 01, 2006 6:06 PM
Subject: Re: Air Getting into Cooling system

> head gaskets are fine, already checked that.
>
> John