You may be lucky and only have a bad radiator cap but this is a firm
indication you are getting combustion gasses into the cooling system. At
speed the suction from the pump is helping to keep the coolant down but as
the engine slows down combined with the heat soak the coolant expands out it
comes.

In a pinch you can use a regular VW pressure cap readily available, (without
the overflow hose). It just vents around the cap. There will always be some
expansion space in the pressure bottle but this will work fine if nothing
else is wrong.

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Tom Rowsell
Sent: Monday, August 22, 2011 2:09 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Coolant Strangeness

This is likely an FAQ...I'm on the road and searching is awkward with cell
phone.
It seems when I drive for an hour or so at highway speed, and stop abruptly
(to get gas for example) coolant rushes from the left tank into the overflow
one on the right, sometimes overflowing that one onto the ground. In one
instance the dash light began to flicker and when I pulled over, the right
hand tank was full, and the left one was down 1/2 litre or so. It's not
overheating, but temperature rises at idle after a highway run.
2.1 litre, recent (last 6 months) new rad, water pump. There are no evident
leaks, and oil on dipstick looks clean.
Any suggestions on what to check?
The needle is generally parked right at the center of the LED...
Thanks
Tom