coolant system corrosion

following from the recent thread on this topic, it seems there are some fundamental misunderstandings out there that need to be cleared up.

the first thing to understand is where corrosion comes from in the first place. very simply, it comes down to electrolysis. remember when you made a battery in school with a strip of zinc, a strip of copper and a lemon? well, that works because of the difference in electrode potentials between the two metals, and the presence of an accommodating electrolyte.

in car cooling systems, you have different metals used, iron, aluminum, copper, etc., and you have an electrolyte, the fluid in the cooling system. [there is more than that, but i'm simplifying for illustration]. so, that's going to lead to corrosion!!! how do you stop it?

basic methods:

  1. remove the electrode potential difference as much as possible - use an aluminum radiator with an aluminum block for example.

  1. passivate the materials as much as possible - slows thing down.

  2. use a non-electrolytic coolant fluid.

used together, all these work well and cooling systems can last many years with no obvious or at least, minimal degradation.

but what are the practical realities?

a. people tend to introduce electrolytes into their cooling system - the use of tap water being the prime example. not great, but it's life. and cars don't last forever.

b. use of the above can in fact cause some passivation. for example, buildup of calcium carbonate in a cooling system can slow down corrosion rates since it interferes with electron flow. but it also interferes with heat transfer, a strongly negative and unwanted side-effect. again, not great, but it happens. indeed, as a passivation strategy, silicates were use as a corrosion inhibitor in cheap antifreeze for this reason - it passivated the system by coating it. [but it also coated and ruined pump seals]

c. when, inevitably, a cooling system treated as above becomes too inefficient and fails and a radiator is replaced, the new radiator can fail rapidly afterwards. why?

this last seems to be the big problem that's confusing, even to experienced and otherwise very knowledgeable vehicle techs, and it seems it's being misattributed to use of de-ionized water as antifreeze dilutant.

how can this be? because there is essentially no difference between distilled and de-ionized, and certainly not for this application.

let's go back to what we know from the above:

electrolysis. electrode potentials for copper, iron and aluminum are ranked in that order. iron is more active than copper, but aluminum is more active than iron.

if you have an iron engine block, and a copper rad, even if you use a coolant full of electrolytes, the dissolution takes place primarily in the most active component, the iron. and with some considerable thickness of iron to eat through, you're really not going to notice any problems most of the time.

so why did the new radiator fail?

most new radiators are aluminum. so, as we learned above, now it will be the one that corrodes, not the iron. and, this aluminum is /real/ thin.

but we just used de-ionized water - didn't that cause the problem? nope

- there's no difference between that and distilled. not true de-ionized anyway. some products are sold as producing "de-ionized" water, but they're mis-described, and are merely water softeners, not de-ionizers. [and their product is highly corrosive].

remember that this is a repair of an existing system? well, that engine is full of years of corrosion product. you didn't care about it before, but now, unless your new antifreeze contains sufficient concentration and efficacy of corrosion inhibitors, all those products are going to re-equilibrate back into the coolant and become an electrolyte and provide the means for the corrosion to start. did we use a chemical de-scaler or coolant flush as part of the replacement? then magnify this effect even further because those chemicals are very aggressive and very hard to completely remove.

bottom line: if we want to avoid surprises like this, we need to understand the principles of what's happening.

i. replace like with like wherever possible. your system reached something close to an equilibrium as it stood before. if you change that, and complete electron flow reversal like swapping a copper radiator for aluminum on an iron engine block will do that, is about the worst thing you can do.

ii. use the best quality antifreeze with a decent corrosion inhibitor package. don't use "filtered" or recycled crap.

iii. consider very carefully before using a chemical flush of the system. no matter how you try, chemicals will remain on the metal surfaces and come back out into the new coolant fluid to act as electrolyte and facilitate corrosion. in extreme cases, it may be better to use them than have a system full of scale that's overheating, but if doing so, observe #i above. personally, i recommend leaving flush chemicals alone in aluminum systems unless you have no other choice. [use of decent coolant/dilutant will usually avoid all need for this though.]

iv. use high quality replacement parts! internal passivation and corrosion resistance varies. cheap stuff is cheap for a reason!

v. understand what's going on. don't misattribute a failure to the wrong cause [for this application, there is no difference between distilled and true de-ionized]. you'll spend a bunch of money and you'll have the same problem coming back again and again.

vi. don't mistake the difference between de-ionized and softened water.

Reply to
jim beam
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I thought I would find some issues with you here, but your points are not at all bad.

"Electrolysis" is a catch-all word that people use instead of electrochemical explanations.

It is not an all inclusive term.

Galvanic corrosion often occurs when metals of two unlike redox potentials are connected with an electrolyte as the external current path.. Basically what you said, but a little more detailed.

Electrolysis may also take place when corrosion currents occur from sources other than galvanic contacts.

Corrosion inhibitors CAN reduce corrosion enormously by modifying the surface matrix on a metal, in contact with an electrolyte.

Triple distilled water (or GOOD deionized water) can be a wise choice instead of tap water that may be laden with a plethora of minerals.

Aluminum is a strange one. When properly anodized, it can be relatively corrosion resistant. When that film is broken, aluminum is not worth a darn as a corrosion resistant metal.

Worthwhile post, Jim

Reply to
hls

thank you. difficult to condense major scientific principles into just a few paragraphs.

Reply to
jim beam

Absolutely.

Reply to
hls

[accessible] further reading:

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Reply to
jim beam

"hls" wrote in news:L_udnaGFv_g2P5LRnZ2dnUVZ snipped-for-privacy@giganews.com:

Not being a chemist, I solved this quandary by simply following the specific directives of the engineers that designed my engine and/or its OEM fluids. I decided that they are quite likely to know best exactly what will prevent my engine's cooling system from corroding. And you know what? The advice I've followed has been spot-on.

Reply to
Tegger

what do those engineers say for the conditions under which to check the oil level on an integra?

Reply to
jim beam

I am sure they know what is best, but I am not sure that they always specify what is best. DexCool, IMO, was not necessarily the great inhibitor package it was cracked up to be, and I am sure there were political reasons for its choice as much as, if not more than, performance reasons.

Sometimes a company "buys into" a certain technology, and they push it (until it pushes back).

Especially during the warranty period, there is some wisdom in using what the manufacturing company specifies.

Like we have discussed in previous oil threads, coolant packages are not usually accompanied with hard scientific data that would let you know what the actual performance criteria are. Lots of testimonial and hype, but seldom any hard data.

Reply to
hls

"hls" wrote in news:Be2dne_S-eyuxojRnZ2dnUVZ snipped-for-privacy@giganews.com:

Not to you, no. Not to you.

Reply to
Tegger

Thanks for the treatise Jim, good stuff.... I always check the coolant with a volt meter, and have seen as much as

6 volts from the coolant to ground. If a flush and fresh coolant wont eliminate the voltage, I'll add a ground strap from the radiator to the body and engine. In stubborn cases, and with plastic radiators, I'll add 'Napakool', a coolant additive until the volt meter tells me to stop. Just my unrequested 2 cents worth.... Ben
Reply to
ben91932

Yes, I want data, not testimonial and hype. Nothing wrong with that, now, is there?

Reply to
hls

it's not "hard", but it's more informative than normal "hype"...

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Reply to
jim beam

At one point, several years ago, I worked on formulation and testing of this type of corrosion inhibitive packages, as well as others. That is why I keep singing the song of wanting data.

We actually bought the DexCool package and used it for bulk glycol deliveries. It wasnt so very great, but it was ****biofriendly**** which is what the customer wanted.

It was not a matter of "not invented here".

There is often a tradeoff when trying to field ecologically "green" materials. Usually they dont work as well as the optimum technology that can be formulated, but there is money to be made with them on the market.

People are often afraid of "those dangerous chemicals" without knowing what they are and what dangers, if any, are involved.

Thanks for the link

Reply to
hls

can you share any links to the testing you did?

Reply to
jim beam

Looking for hard data of this type in a Usenet group is probably wrong on a couple of levels. A trade journal would be a better place to start, or would it? :-)

Reply to
dsi1

I wish I could. It is held within the company in my laboratory notebook archives, and in reports to the customer (Statoil Norway). That is where a lot of technology is "hidden" and it is why it is so hard to access.

A lot of this is not patented, but is disclosed so as to be able to prove prior art. A patent is just a clue to the competitor as to what you are doing.

I do hold some patents, but we were encouraged not to patent.

We tested both with linear polarization resistance instruments(where applicable) , and with prepared metal coupons of all the typical metals and alloys that would be encountered within a system. The coupons were evaluated by weight loss, surface condition and matrix, embrittlement tests, etc.

Tests were done with and without oxygen for extended periods, as you would encounter in cooling systems from time to time.

Short term tests often give promising results, but as the system ages, as it would in application, some of the inhibitor components decompose, are precipitated, or are otherwise deactivated.

Aluminum is perhaps the hardest nut to crack. Once it starts corroding, it is hard to stop. Organic acid technology didnt seem to be too good for this, compared with the industry standard silicates.

Pinhole, crevice, and other very locallized modes of corrosion sometimes take a while to show up in testing, leading one to think that the system is well protected. But in time, when the inhibitor package allows it to happen, failures can be rapid and catastrophic even though most of the system looks pristine.

We introduced, by the way, the first biodegradable nontoxic corrosion inhibitor to the North Sea area. It was good, but not great, but beat everything else in the market, and is still being sold.

These coolant packages are used not only in automobiles but in coolants for industrial applications of many types.

Reply to
hls

Reply to
dsi1

"dsi1" really doing because all that info is proprietary and closely guarded.

Im afraid so...that the salesmen dont necessarily have the real info on the products.

People are so worried about suits, proprietary information, etc, AND justifiably so.

Nowadays, with the instrumentation we have, it is impossible to hide a secret about chemical formulations. What is harder is to learn the process one might use to make those chemicals.

Would you believe that the process to make ethylene oxide, the precursor to ethylene glycol antifreezes, only yields 1-2% product on each pass through the plant? It is true. BUT, in an enormous plant, 1-2% can yield millions of pounds of product per year.

I have been in this business for 45 years, and am still learning. When I graduated from the university, I thought I knew every chemical reaction known to man. My first boss, a lady, told me that " now it is time for you to learn some chemistry". She was right, and I have been at it ever since.

Thanks for your post.

Reply to
hls

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