Date:         Fri, 30 Jun 2006 12:00:00 -0700
Reply-To:     Alistair Bell <albell@UVIC.CA>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Alistair Bell <albell@UVIC.CA>
Subject:      another discussion point on coolant system corrosion
Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed

Hi,

the recent discussion about using other metals in the cooling system,
ie stainless, copper, had me thinking about stainless in the vanagon
cooling system.

Now, I am just throwing this out for discussion:


In the scale of "activity" for metals, aluminium is more reactive
than stainless, that is stainless (various grades differ) can be
called more "noble" than Aluminium (imagine gold being most noble and
magnesium the least).

Both Al and SS  rely on a quickly formed oxide layer that resists
further oxidation. So both are great for use in many environments.

But, and I have seen this happen more than once, If Aluminium and
stainless are joined together, example being stainless bolts in an
aluminium structure, and if there is an electrolyte (salt air,
coolant etc), then the more noble stainless will gain electrons and
the aluminium will lose them (oxidation).

I saw this first hand last fall in a large bike rack I made for a
local company. They needed something to get the bikes out of the way
in a covered passageway at a marina (where their offices were). My
friend and I made a hanging rack from stainless track, aluminium box
section, all welded and or bolted (ss) together.


The rack was only exposed to salt air, no spray or rain. But a few
weeks later when we did some adjustments, there was powdery corrosion
on the aluminium under the stainless bolts (washers). We needed to
add some nylon washers to try break the electrical path.

The surface area of the sacrificial metal, Al, was much, much greater
than the "gaining " metal stainless. Imagine the corrosion if it were
the other way around, or imagine someone using aluminium pop rivets
in a stainless structure exposed to salt air or spray, the rivets
would be corroded away in no time.



Now god only knows what goes on in the vanagon cooling system, which
metals in that environment become more noble. Sticking a few square
feet of stainless into the mix MAY not be as benign as one would
imagine.

Anyhoo, its a good topic for a chat over a few beers.

Alistair


'82 westy, diesel converted to gas in '94
http://www.members.shaw.ca/albell/