Date: Tue, 2 Nov 2010 09:05:29 -0700
Reply-To: Alistair Bell <albell@SHAW.CA>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Alistair Bell <albell@SHAW.CA>
Subject: Re: A response from Prestone about Stainless Steel Pipes
In-Reply-To: <4CD02EC1.8080407@comcast.net>
Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed
Hey, I don't take it as a personal attack, but feel free to knock me
down a peg or two if I start spouting more Feynman or Fermi quotes :)
The engine alloy is the question. I didn't have a bit lying around to
use in test. I am thinking it has at least Silicon in the mix,
perhaps Mg too? This is pure speculation, but the alloy may have been
chosen for reasons other than corrosion resistance. You notice how
bad some engine and tranny exteriors look?
What I have concluded after all the discussion about this topic, and
my wee experiment, is:
1. its an undeniable fact that aluminium is much more of an active
metal than any type of stainless.
2. if the metals are electrically connected and share the same
electrolyte, then dissimilar metal corrosion will occur, with the
aluminium being the anode and oxidised.
3. the anti corrosion additives in modern coolants - and I used an
OAT based (ie Dexcool or "long life" type) - will prevent the
corrosion on the aluminium.
4. the coolant in our vans is, on average, not changed often enough.
The whole subject of dissimilar metal corrosion in a complicated set
up such as the vanagon cooling system is full of unknowns and is ripe
for fantasy ideas.
1. what is happening when you get corrosion under an O-ring or
gasket? Is it a stagnant area where the coolant is depleted of its
anti corrosion additives? Or, (and this is really wild speculation),
does the carbon black filler in rubber O-rings act as the noble
metal? Carbon is close to the top, if not at the top, of most list of
noble metals.
2. does the anoxic environment of the system cause any stainless
steel present to change into its active form (loss of protective
oxide layer). If so, this might be an advantage, lessening the
galvanic differences between stainless and aluminium.
I will take pics of the metal samples today, and I will post on my
blog as well as the previously mentioned samba blog.
Oh one more thing.... I can understand how vendors of stainless pipes
might feel a little uneasy with this discussion. Ken, you are the
first vendor that actually seems to care and do some research rather
than reflexively attack or dismiss the whole idea. Good on you Ken, I
mean it.
alistair
'86 syncro 7 passenger
'82 westy, diesel converted to gas in '94
http://shufti.wordpress.com
On 2-Nov-10, at 8:31 AM, Ken Wilford wrote:
Alistair, I am happy you are doing this experiment. Just so you know
all the the stainless lines that I have sold and seen are 304
stainless. So your test should be good. Not sure what alloy the
Vanagon engine case is though.
PS I didn't know you were doing this so please don't take my post as
some type of personal attack on you. I respect folks who are willing
to test things. Just not folks who only speculate.
--
Thanks,
Ken Wilford
John 3:16
www.vanagain.com
Phone: 856-327-4936
Fax: 856-327-2242