Alistair,

I'm moved to enter the fray as the prospect of a technical, engineering, even scientific egad chemical discussion with obvious interest on the list is just too enticing to pass up!

To wit, as you well know, the initial and potentially sustained measurement of current in the simple experiment answers and verified the original question. Namely if current is flowing, corrosion is occurring. Some substantial fraction of the current will result in metal dissolution and ion injection. As many have strongly suggested, the dastardly real world is quite complex and many competing processes are occurring.

However, Tom has offered the one true limiting answer. In all dissimilar metal systems interconnected by by a conductive liquid, corrosion will occur. The real world cooling system is not deoxygenated. All that can be done in the glycol/water system (irrespective on the chemical nature of the glycol) is to add a variety of surfactants which will impede the kinetics of the process. This holds true even for propyl glycol mixtures with 18 M-ohm water. The extent of the corrosion is limited only by the cross-product of the reference current flow and the time observed. Generally the observational time is limited by a collision or fiscal trauma.

As Tom pointed out, the only answer in any liquid phase interconnected system is the use of sacrificial electrodes. Zinc is the usual metal of choice and aftermarket pellet systems are readily available to insert into the radiator holding tank, or the inlet plumbing leading to the radiator. Electrical connection to the engine block is essential but often unavoidable. Typical slave electrodes are changed out every 50,000 miles or 2 years in the trucking industry. The net effect is a modest increase in salt concentration in the coolant. A secondary effect if added early in the vehicle's life cycle is very clean internal surfaces and good thermal transfer. This does not impact pH derived corrosive attack, plasticizer leaching from polymer hoses, inversion of vulcanization reactions due to sulfur extraction from rubber compounds in hoses, etc., etc.

As a bemused side note, I was once very concerned about poor thermal transfer in my '50 Mercury flathead engine cylinder head. Inspection of the inner water passages showed an oxide laden very roughened surface structure. I decided to chemically etch the interior with alternate treatments of strong acid, then strong base. I then attempted to electropolish the interior. I made up an electrode assembly with a heavy copper wire with a 1 or 2 mm insulating jacket that I punched holes through to expose the wire. The idea was to be able to snake the wire through the coolant passage without shorting the system to the interior walls. I used alternating voltage electrolysis to attempt to remove asperities and smooth the interior. Made a hell of a mess in the lab but removed a significant amount of cast iron. I was surprised to find small clusters of iron nodules and lots of carbon in the effluent - a testament to the foundry conditions of the time. Of course significant amounts of silica were released as well. Finally concluded I had gone as far as I dared and cleaned up the system and bolted the engine back together. Try as hard as I could, I could measure no thermal difference in the performance of the head or the engine. Finally admitted defeat and went off to the Victory Pig for pizza and a beer. Never again, I said. ... Until the next time!

Frank Grunthaner

-----Original Message----- From: Alistair Bell <albell@SHAW.CA> To: vanagon@GERRY.VANAGON.COM Sent: Tue, Nov 2, 2010 10:19 am Subject: Re: A response from Prestone about Stainless Steel Pipes

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 ------------------------------------------------------------------------ ---- ---- No virus found in this incoming message. Checked by AVG - www.avg.com Version: 9.0.864 / Virus Database: 271.1.1/3232 - Release Date: 11/01/10 12:34:00 _____ No virus found in this message. 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