dennis

thanks for the informative post.  i would like to say in reguards to the
main expansion tank not being large enough, that in my practical experience
that is not true.  i have been running a self built 15 degree digifant
engine conversion for over 10,000 miles, in various climates and
altitudes.  the system that i have designed is very similar to the golf
system (no over flow tank) except that i am using the vanagon expansion
tank as my expansion tank.  on this tank i use golf style cap without the
coolant expansion nipple/valve.  i run the system with about a 1/3 or 1/4
of the expansion tank containing air.  the tank is mounted at about
cylinder head height.  i have been through most types of driving
conditions including a 5,000 mile trip from michigan to the pacific
northwest.  in that time i have had no problems with the tank being air
bound during cold or it over flowing when hot.

i would like to take this issue of entrained air a bit further i have read
in the past technical papers and power point presentations referring to
the possible cavitation, and internal pitting and corrosion.  the stuff i
remember reading was write up pertaining to large diesel engines such as
those in trucks.  if you have or know of any references on this subject i
would be interested to know of them.  also if this is a problem in engine
situations why does volkswagen and other manufacturers continue to use
this type of set up?

jonathan

On Mon, 8 Mar 2004, Dennis Haynes wrote:

> The major difference is the capacity of the cooling system. The golf has
> less than 2 gallons of coolant where the vanagon carries almost 5. The
> main expansion tank is not large enough to allow for this without
> becoming air bound when cold and overflowing when hot so the second tank
> is needed. The second tank being downstream of the relief valve allows
> adding make up coolant without opening the system. Many cars are set up
> this way. Another advantage is that without air in the pressurized
> system, the coolant is less likely to carry entrained air/O2 which
> avoids cavitation, internal pitting and corrosion.
>
> Dennis
>
>
>
> -----Original Message-----
> From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf
> Of Jonathan Farrugia
> Sent: Monday, March 08, 2004 4:05 AM
> To: vanagon@GERRY.VANAGON.COM
> Subject: Re: cooling system design
>
> okay i understand that, thats basically a description of how the vanagon
> cooling system operates.  what i was trying to get at in my first post
> which re-reading it i see i didn't convey.  is that the golf system
> doesn't have the second over fill tank it only has one expansion tank
> with air in it.  the golf tank has two hoses attached one that routes to
> the water pump allowing the water pump to draw from the expansion tank,
> and another small hose about 5/16" that routes coolant form the top of
> the radiator into the expansion tank.  under operational conditions the
> small 5/16" hose provides a steady stream of coolant from the top of the
> radiator to the expansion tank.  upon cool down the golf system draws
> atmospheric air into the expansion tank if i needs to balance the vacuum
> on the cooling system.
>
> what i want to know is what are the technical differences between these
> systems, i.e. contrast comparison of the systems.
>
> jonathan
>
> On Mon, 8 Mar 2004, Daniel L. Katz wrote:
>
> > 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
> >
>
>
>