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  #1 (permalink)  
Old 08 Jun 2010, 02:43 pm
jim beam
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Default 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.

--
nomina rutrum rutrum
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  #2 (permalink)  
Old 08 Jun 2010, 05:04 pm
hls
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Default Re: coolant system corrosion

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


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  #3 (permalink)  
Old 08 Jun 2010, 05:56 pm
jim beam
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Default Re: coolant system corrosion

On 06/08/2010 03:04 PM, hls wrote:
> 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.


--
nomina rutrum rutrum
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  #4 (permalink)  
Old 09 Jun 2010, 09:18 am
hls
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Default Re: coolant system corrosion


"jim beam" <me@privacy.net> wrote in message
>>

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

Absolutely.

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  #5 (permalink)  
Old 09 Jun 2010, 10:40 am
jim beam
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Default Re: coolant system corrosion

On 06/09/2010 07:18 AM, hls wrote:
>
> "jim beam" <me@privacy.net> wrote in message
>>>

>>
>> 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/th...id/591732.html


--
nomina rutrum rutrum
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  #6 (permalink)  
Old 10 Jun 2010, 11:59 am
Tegger
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Default Re: coolant system corrosion

"hls" <hls@nospam.nix> wrote in
news:L_udnaGFv_g2P5LRnZ2dnUVZ_uGdnZ2d@giganews.com :

>
> "jim beam" <me@privacy.net> wrote in message
>>>

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

> Absolutely.
>



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.


--
Tegger
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  #7 (permalink)  
Old 10 Jun 2010, 01:26 pm
jim beam
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Default Re: coolant system corrosion

On 06/10/2010 09:59 AM, Tegger wrote:
> "hls"<hls@nospam.nix> wrote in
> news:L_udnaGFv_g2P5LRnZ2dnUVZ_uGdnZ2d@giganews.com :
>
>>
>> "jim beam"<me@privacy.net> wrote in message
>>>>
>>>
>>> thank you. difficult to condense major scientific principles into just
>>> a few paragraphs.
>>>

>> Absolutely.
>>

>
>
> 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?

--
nomina rutrum rutrum
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  #8 (permalink)  
Old 13 Jun 2010, 05:26 pm
hls
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Posts: n/a
Default Re: coolant system corrosion


"Tegger" <invalid@invalid.inv> wrote in message
>
> 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.


> Tegger


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.

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  #9 (permalink)  
Old 15 Jun 2010, 07:04 pm
Tegger
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Posts: n/a
Default Re: coolant system corrosion

"hls" <hls@nospam.nix> wrote in
news:Be2dne_S-eyuxojRnZ2dnUVZ_tydnZ2d@giganews.com:


>
> 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.


--
Tegger
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  #10 (permalink)  
Old 17 Jun 2010, 03:25 pm
ben91932
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Default Re: coolant system corrosion

On Jun 8, 12:43*pm, jim beam <m...@privacy.net> wrote:

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

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