as the engine cools the pressure drops in the expansion tank and coolant
is pushed up to the expansion tank from the overflow tank, which is always
at atmospheric pressure. air buoyed up on top of coolant in the expansion
tank reduces this pressure drop, but this air tends to get pushed out when
hot, expanding coolant flows out toward the overflow tank.

dlk

On Mon, 8 Mar 2004 01:47:38 -0500, Jonathan Farrugia <jfarrugi@UMICH.EDU>
wrote:

>i am interested in having a discussion about different types of cooling
>systems.  specifically the design benefits and difference between the
>types of cooling systems in other vw's and the type of cooling system in
>the vanagon.  for point comparison we could use the 85-92 golf.  that
>system has a expansion bottle with air in it, the air is at the highest
>point in the system and it the system operates fine.  where as in our
>vanagons we have a completely filled system with no air.  what is the
>technical problem with having a little air at the highest point in the
>system or in an expansion bottle.
>
>if there is a technical name for systems with air and systems without air
>i would be interested in what they are called.
>
>jonathan