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.

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

3. 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.

 

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

 

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

 

Absolutely.

 

[accessible] further reading:

http://www.eetcorp.com/antifreeze/antifreeze-faq.htm

http://answers.google.com/answers/threadview/id/591732.html

 

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.

 

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

 

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.

 

Not to you, no. Not to you.

 

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

 

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

 

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

http://www.eetcorp.com/antifreeze/antifreeze-faq.htm

 

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

 

can you share any links to the testing you did?

 

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?

 

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.

 

Some industries are more open than others. Occasionally you will find
articles in some trade journals, or in the periodicals of associations like
the National Association of Corrosion Engineers.

I suppose that companies which market coolants either think we are too
stupid to appreciate test data, or it is a practice that they really dont
want
to get started.

 

Unfortunately, most of us are too stupid to appreciate test data, you're
not, but that doesn't matter much anyway because it's not in the best
interest of the companies that market coolants to release hard data that
has not been spun to favor their products. That's the breaks.

Hearing aid companies have all kinds of schemes to reduce noise and
increase comprehension of their products. The dirty little secret is
that the people selling hearing aids don't know what their products are
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.

 

Or,
1) buying a car from a reputable and successful automaker that is not
currently owned by a union or a government, and
2) following that automaker's maintenance and repair instructions, on the
premise that they're probably pretty good at what they do, otherwise you
wouldn't have spent good money on their product.

Personally, I find that 1 & 2 work fairly well when one is not in a
position to be able to discern whether or not any given chemist (or
chemist-wannabe) is talking rot or not.