Date:         Wed, 29 May 1996 11:48:51 -0300 (ADT)
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         smitht@jupiter.sun.csd.unb.ca (Tim Smith)
Subject:      [vanagon] ceramic caotings/corrosion

>carrying away metal, I figure it starts this way in the Vanagon then the
>electrolysis takes over.  An interesting point to back this up is that
>Leonard
>at AVP was telling me once that in the 100's of Wasserboxer heads of
>various
>conditions they have seen, it always appears that the problem DOES NOT
>start
>at interfaces between the dissimilar materials like it should if
>initially electro-
>chemical in nature but rather away in the head off by itself and often
>the studs are not corroded either.  As the electro-chemical corrosion
>is only going to happen between metals of different potential, if it
>does not start there, we must look for another reason.  All big trucks
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

I put a longish posting up on this a while back, try the gopher.  Vanagon 
corrosion is electrochemical based, ALL corrosion is.  Dissimilar metal 
create a galvanic cell yes, but not in the vanagons.  Your friend Leonard 
has noted correctly, the corrosion is up on the heads UNDER the thick rubber 
gasket.  This is caused by the thick rubber gasket allowing coolant to seep 
under it when under pressure.  This forms little pools of trapped coolant 
and it is the concentration of ions and depleted oxygen that's causing 
electrical gradients to form. This is referred to as CREVICE corrosion, and 
any book on corrosion will cover it in detail. The book will also tell you 
NEVER use compliant gaskets in a system subject to corrosion. Plain and 
simple, VWs designer screwed up on this. They were mechanical engineers, not 
corrosion types.
          The wasser engine is based on the cylinder barrels being clamped 
under high pressure between the block and the heads, using thin gaskets 
(yes, I know there is an O-ring there, and it corrodes nearby same way! just 
much more slowly). The water jacket surrounds this system, but since it is 
aluminium it expands more than the steel barrels when hot, so it needs room 
to grow.  Hence the thick rubber gaskets that cannot be highly compressed 
(they shred) as they are there to act as compressible/moveable seals.  The 
problem is a design flaw, plain and simple.
        If you want to prevent it, apply a coating, VW now uses cadmium, 
giving that goldish tint that is totally worthless longterm in an automotive 
environment. It has also been banned in parts of Europe due to enironmental 
toxicity.  You might try an epoxy based paint, medium temp and aluminium 
compatible. Mechanic near me fixes head, 7 vans, 14 heads so far, using 
JBWeld as sealant over pitted surfaces. No recalls, first one has done 120K 
kms (75K miles) since repaired.  Clean up the head pits, sandblast, goop 
with JBWeld and reassemble with new gaskets. 
        In summation, no active anti-corrosion system is going to do squat 
for head corrosion, nor is using the "highest quality" engine studs that the 
guy from Racewares is pimping as a wasserboxer cure-all on the rec.VW.H20 
list. Learn to live with it, flush coolant regularly, maybe even annually.  
And try a good anti-corrosion coating on your new heads when rebuilding, or 
epoxy fill-coat on bad used ones.


Tim Smith