Date: Tue, 2 Nov 2010 10:19:41 -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: <008b01cb7ab1$64c1e5a0$2e45b0e0$@net>
Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed
Tom,
- carbon is more noble than either Al or stainless.
- I would not expect the Al in my test to be shiny if corroded, I'd
expect a white deposit similar to what Ii have seen in other similar
situations.
- the metals were electrically bonded in my experiment
- i don't think there are any metals in the vanagon system less noble
than the Al alloy in engine.
alistair
On 2-Nov-10, at 10:14 AM, Tom Hargrave wrote:
I was wondering if someone was going to bring up rubber hose
corrosion. It's
the number one cause for hose failure.
Also, you'll notice that hoses that are failing always bulge at the end,
like just before its connected to the radiator. This is no
coincidence - the
hose corrodes the fastest close to the opposing pole. The corrosion
weakens
the hose then inner pressure causes swelling.
Also, it was mentioned that the aluminum in the test was still shiny.
This
is actually a bad sign - the metal being eroded away will remain nice
and
bright and shiny!!!!
I suggest you weigh the two parts before the test. Then pull them out
and
dry & weigh them after the test. You may find that a perfectly normal
part
has lost mass which would indicate that the surface is slowly corroding
away.
The least noble metal should be the one that corrodes and in the case of
stainless steel and an aluminum alloy, the least noble will be the
aluminum
alloy. But in a cooling system where you have mixed metals and hose, the
least noble may be the carbon in the hose. In other words the test is
not
replicating real world.
In other words, to replicate real world you need all of the alloys that
touch each other bonded together - not just two. When done right only
the
least noble metal will corrode.
Salt water mechanics understand this. They will tie everything
conductive
together then connect a wire to a zinc anode. When done right only
the zinc
will corrode because its less noble than even aluminum.
Thanks, Tom
www.towercooler.com
From: Vanagon Mailing List [mailto:vanagon@GERRY.VANAGON.COM] On
Behalf Of
Zolly
Sent: Tuesday, November 02, 2010 11:44 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: A response from Prestone about Stainless Steel Pipes
Well, earlier experiences show that the Carbon in the rubber is the main
cause of the corrosion activity at the head gaskets, where the aluminium
oxide builds up and pushes the parts apart well enough to let coolant
out.
Being the largest rubber in the system, is why we see that happen more
obviously than other areas such as the water pump O ring.
I think, the stainless is a much lesser problem than any other metal
around.
Zoltan
----- Original Message -----
From: "Alistair Bell" <albell@SHAW.CA>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Tuesday, November 02, 2010 9:05 AM
Subject: Re: A response from Prestone about Stainless Steel Pipes
> 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
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