Date:         Fri, 1 May 1998 13:52:17 -0700
Reply-To:     Malcolm Holser <mholser@ADOBE.COM>
Sender:       Vanagon Mailing List <Vanagon@vanagon.com>
From:         Malcolm Holser <mholser@ADOBE.COM>
Subject:      Re: Cavitation corrosion/erosion
Comments: To: Vanagon@VANAGON.COM, rstevens@ISLANDNET.COM

Very interesting.  Probably not applicable to our VWs but still
interesting.  First, this is of greater concern in diesels, where
the *normal* operation is "knocking".  The problem is that the shock
wave from the detonation causes ringing in the cylinder sleeves.
Gasoline engines should never experience this.  Secondly, I have
never heard of cylinder corrosion as being the big problem on
Vanagons -- rather it is the corrosion of the heads.  Vanagons, more than
any other engine of my experience, are highly susceptible to the
*other* major corrosion player -- galvanic corrosion, which occurs
when dissimilar metals are in electrical contact and immersed in a
conductive fluid.  Our Vanagons have Aluminum heads, iron cylinders
and magnesium cases -- a real horror!

Cavitic corrosion can be really interesting -- I have seen almost
unbelievable pits on ship propellors, where the very nature of the
beast promotes cavitation.  The subsequent pits result in more cavitation,
and lines of holes eat their way deep into the propellor.  This probably
occurs in our water pumps, but they are pretty easily replaceable.

The material they speak of might not be good in such a mixed-metal engine.
It might be fine -- I have no idea, but very few parts (mainly the
cylinder sleeves) would be protected, and it might attack other parts of
the engine -- such was hinted at in the article.

Malcolm