Warning LONG:
Roland brought up the issuue of using Antifreeze at all in places where
it never gets below freezing and I agree. I wrote this for the local
Jaguar club earlier this year...
ETHYLENE GLYCOL: Ethylene glycol is a clear colourless, odourless liquid
which has the property of both lowering the freezing point and raising the
boiling point of water. It's ease of handling makes it a convenient and
popular anti-freeze. World-wide approximately 6,700,000 tons of ethylene
glycol is manufactured every year, about 50% of this is used as anti-freeze.
At about $2-8 per litre (tax-free, direct from a chemical company) you can see
that glycol production for antifreeze purposes is big business. Another 40%
is used in the fibre industry to manufacture polyester. This turns up mainly
as clothing and recyclable plastic bottles. The final 10% of uses are as
hydraulic fluid, solvent and a plasticizer. In other words ethylene glycol is
used in cooling systems, paints, plastics, clothing, hydraulic systems,
cosmetics and in some unfortunate instances, french wine.
In the context of the automotive cooling system ethylene glycol is not an
anti-corrosive agent, it is in fact corrosive. To offset this fact
manufacturers add anti-corrosives (inhibitors) to the glycol mix/preparation
(usually 30% ethylene glycol + inhibitor formulation and 70% water). These
preparations while in good condition perform well in their intended role in
both minimising corrosion and preventing freezing of the coolant, however,
over the life of the coolant the anti-corrosion properties of the inhibitors
are depleted. Once they fall too low you may have a coolant that is acidic
(containing among other things oxalic acid) which is corrosive to metals.
I should mention that plain water is also a corrosive if used alone in your
cooling system, however, water is corrosive for different reasons than glycol,
as will be discussed later. Let's consider the two properties of ethylene
glycol that are of concern, toxicity and corrosiveness.
1: CORROSIVITY: The terms "glycol", "inhibitor" and "coolant" are often used
interchangeably and hence confused, in the context of automotive cooling
systems. There are important differences, a coolant has the task of
transferring heat from the engine through some type of heat exchanger
(radiator) to the air. Almost any liquid can serve as a coolant. However
a good coolant should also minimise corrosion damage to the cooling system.
Water and Glycol alone or in combination may both serve as coolants as they
are liquids. An inhibitor has the role of minimising or preventing corrosion
that is often caused by coolants. Both water and glycol alone or in
combination are corrosive and need inhibitors added to them to prevent
corrosion.
Water aids corrosion in three main ways; 1) bringing free oxygen in close
contact with the metals so that corrosion (oxidation) can occur. 2) Water is
conductive, once water has been flowing in your cooling system for some time
it's conductivity will rise as it picks up metal ions and the water may serve
to promote electrical activity which may erode metals by galvanic action.
3) Some of the metal ions in the water may also react directly with the metal
surfaces.
Why is glycol corrosive? Apart from supporting the above three processes
ethylene glycol has the added unfortunate property that it oxidises through
several stages to oxalic acid. Most of the series of oxidation products to
and including oxalic acid are directly corrosive to metals. Added to this,
oxalic acid is highly toxic. Conditions conducive to breakdown of ethylene
glycol into corrosive acids are present in an engine cooling system. These
include heat (specifically engine hot-spots), galvanic or electrolytic
couples of the several metals that are in the system, occasionally the
presence of combustion gasses, water impurities and elastomer additives.
If you overheat (boil) glycol based coolants they must be replaced immediately
as this accelerates the oxidization process of the glycol to acids. For the
thrill-seekers among you the products of ethylene glycol oxidation by oxygen
and subsequent reactions include: aldehydes, carboxylic acid, nitric acid
, glycolic acid, glyoxylic acid, oxalic acid, formaldehyde and formic acid.
To combat the above acids and other corrosion activity, antioxidants and
alkaline formulations are added to the glycol mix. These include many
compounds which are used in cooling systems where antifreeze properties are
not required and include primary, secondary and tertiary amines; organic and
inorganic phosphates, silicates cresols and other phenolic substances; a wide
variety of sulphur compounds; soaps; alkali metal salts; and borates.
These inhibitors slow down the corrosion process caused by the glycol and the
water. They may coat the metal surfaces and prevent corrosion by
passivation. Passivation is the process where the a protective film forms on
the metal which prevents further contact with the solution. Unfortunately
in all coolant preparations (with or without glycol) the inhibitor system
(during engine operation) is being continuously depleted in the performance of
these actions. For this reason, proper cooling system maintenance is
critical.
One aspect of cooling system maintenance that we can all easily follow is to
minimise "aeration" of your coolant. It is essential to keep your coolant
from aerating as this accelerates the uptake of free oxygen from the
atmosphere. As free oxygen is one of the essential ingredients for corrosion
(by oxidation) the importance of minimising it's uptake is clear. To this end
you should make sure all your hoses are in good condition and clamped tightly
(especially the inlet side to the water pump - to help prevent cavitation)
with high quality clamps. "Closed systems", where an expansion tank and
recovery system closed to the atmosphere is used, also help in this regard.
With respect to the corrosion inhibition properties of glycol based coolants.
In 1972 the US army set up a study to determine the rate at which the
inhibitors in a glycol mix were being depleted. A prime function of these
inhibitors is to provide alkalinity to neutralize the organic acids formed by
the oxidization of the glycol. The test was conducted over a period of
several years in all types of vehicles and showed that in a glycol mix 40% of
vehicles needed attention. Of this 40%, 3% had antifreeze in their systems
that was highly corrosive. In light of this it would seem that a "ideal"
inhibition system would allow you to replenish these inhibitors without having
to completely change the coolant.
2: TOXICITY: We all know not to drink coolant when we are stuck in the desert
dying of thirst, here's why; The projected LD50 (The dose at which 50% of a
experimental population die) in humans for ethylene glycol is around 1.4g/kg.
In other words the minimum fatal dose for a 30% ethylene glycol 70% water mix
is around 200 ml in an adult male and about 40 ml (one large mouth-full) for
a 4 year old child.
Unfortunately some of the corrosion inhibitors added to glycol mixes such as
sodium nitrite or sodium benzoate are even more toxic than the glycol. So,
the truth of the matter is that upon drinking a glycol based coolant you are
likely to die from nitrite poisoning well before the glycol has a chance to
kill you. It has been pointed out that this is unfortunate because there is
an antidote for glycol poisoning, alcohol (I kid you not), alcohol keeps
enzymes busy that would otherwise break down the ethylene glycol into toxic
oxalic acid...now we know why your average radiator mechanic has lasted so long.
Effects of ethylene glycol poisoning: If ingested or inhaled (avoid the
vapour from a hot glycol-infested radiators) in sufficient quantities its
immediate effect is on the central nervous system (CNS) where it can result in
headaches, tremors, drowsiness and convulsions. The short term effects of
high doses includes kidney damage leading to a reduced ability to urinate and
accumulation of liquid on the lungs.
WHY USE ETHYLENE GLYCOL?: Given the above, the question must be raised why
ethylene glycol is used in places where anti-freeze properties are not
required? It has been suggested that one reason may lie in the
internationalising of the vehicle industry.
The majority of vehicle manufacturers are international organizations with
headquarters in the Northern hemisphere. As most vehicles are sold to markets
where antifreeze is essential (North America, Japan, Europe), there is little
economic incentive for manufacturers to re-design for non-freezing climates.
Vehicle manufacturers often treat these places identically to their frozen
cousins and supply their own antifreeze/coolant preparation and specify that
only this product is the only product to be used if you want your warranty to
stay intact.
Many "corrosion inhibitors" not only have glycol but they contain it in
bizzare quantities...
SQ36 for example in Australia comes in a 500 ml bottle containing 25.7%
ethylene glycol. As we know that ethylene glycol is not a corrosion inhibitor
one may ask why SQ36 contains glycol at all? It certainly would not provide
real anti-freeze protection (not that the SQ36 claims to have any anti-freeze
properties) as 128 ml of ethylene glycol (25.7% of 500 ml) when it has been
diluted into approximately 20 litres of cooling system, comes out at a
concentration of about 1/2 a percent (0.64%). To enjoy any real anti-freeze
benefits of ethylene glycol you would need at least 50 times that amount
making a coolant concentration of at least 30% ethylene glycol. As for what
is providing the corrosion inhibition in SQ36? well, that's what the other
"mysterious" 74.3% of the bottle is for (no one can tell me what it actually
contains).
Another reason many local manufacturers may recommend glycol based coolants
could be that they want to avoid damage claims when Mr & Miss Sahara-Desert
take their glycol-free car on a skiing holiday and find next morning that
their engine resembles some kind of metal-ice sculpture. It is easier for
companies to make sure all cars have anti-freeze protection and save the
worry. However, given the case with SQ36 this supposition does not appear
well supported.
In conclusion there is no reason why Australian vehicles must use glycol based
coolants. In fact, when you have glycol in your coolant you add to your
headaches (no pun intended) in that you then have to combat the acids that are
produced when glycol breaks-down. Why not simply forget about glycol
altogether? This is in fact what may people (including myself) have done with
their cars. Fortunately, the alternative coolant preparations are often much
cheaper than glycol and have an excellent performance record.
EVILS OF ETHYLENE GLYCOL:
In short, ethylene glycol (which is an antifreeze and nothing more) is not
required in most of Australia. Glycol has no anti-corrosion properties, it is
infact corrosive. To offset this fact manufacturers add anti-corrosives to the
glycol mix/preparation. Over the life of the coolant the anti-corrosion
properties of the additives are depleted. Once they fall too low you have
a coolant that is primarily oxalic acid which is highly corrosive to metals.
Added to this is that ethylene glycol is highly toxic.
No internal combustion engine on the market today needs glycol in the
cooling system. No engine has been designed to need glycol. Glycol is
simply an antifreeze.
Following are 1) Toxicity and 2) Corrosivity assesments of ethylene glycol.
ALTERNATIVES:
The Tannin and Tannin Phosphate in Flo-Kleen and other similar products,
how does it work?
There are a number of inhibitor products for cars cooling systems that
contain tannin-phosphate as the active component. Flo-Kleen is simply
the brand that I use (for geographical reasons; the company is WA based),
it is no better than any other pure tannin-phosphate based inhibitor brand.
John Deer (sell a tannin-phosphate based inhibitor Australia wide for those
who are trying to track it down). Flo-Kleen is sold interstate however.
Note: Flo-Kleen containd simply tannin-phosphate and a flurocine (dye)
indicatorto make it look pretty.
TANNIN & TANNIN PHOSPATE:
Work in a number of ways...
1. Have buffering properties, which ensure that potentially distructive pH
changes do not occur through the oxidation and reduction of the inhibitor.
2. Their ready reaction with metal ions to form soluble complexes reduces
scale formation.
3. They promote metal preservation.
4. They act as oxygen scanengers, reducing the bulk oxygen concentration in the
closed engine cooling system.
Tannins penetrate oxide deposits, soften and remove them from the metal
surface.A tannin film is then formed on the metal surface protecting against
further
corrosion and cavitation erosion. The phosphate component acts together with
the tannin by assisting in the reduction of scale and pit formation on the
metal surfaces.
The tannins used in inhibitors are produced by the aquious extraction of
certain tree barks and wood materials. Tannins are predominaantly large
molecules possesing a number of flavonoid groups; or galloyl esters of glucose.
Hydrolyisis of these compounds results in the formation of polyhydroxy-phenolic
compounds such as phragllol and gallic acid.
Inhibition action:
The effectiveness in tannin compounds in preventing corrosion is two-fold.
The tannins react with oxygen at the metal surface, and with metal ions formed
by anodic reaction, to form a hard protective film (similar to the inside of a
tea pot). The reduction in anodic sites continues rapidly until the metal
surface is fully protected. Once formed, only small concentrations of tannin
and oxygen are required to maintain the integrety of this film. Scale is
removed by the hydrolyisis products of the tannin, yeilding a di-chelate,
which diffuses into the solution bulk.
Oxygen cavanging:
Tannins also react with oxygen in the bulk solution. In an engine cooling
system, closed to the atmosphere, the concentration of oxygen is reduced to
low levels.
Action of the Tannin Phosphate:
The phosphates prevent scale formation and act as a buffer to changes in pH
within the coolant. Phosphates are well known sequestering agents for divalent
metal ions such as calcium, magnesium and iorn, scale deposits are dissolved
and heled in suspension. Pitting of the metal surfaces is minimised by the
pit-capping action of phosphates.
Electrical Conductivity:
Many commercial inhibitors contain large quantities of inorganic salts and as
a result have a high conductivity. When inhibitors fail (ie when they are
exhausted) their high conductivities can assist high current flows between
dissimilar metals that are already in electrical contact, this results
in rapid corrosion. Tannin and tannin phosphate compounds in a solution
of pure water (reverse osmosis, distilled or pure) have a very low conductivity
and even if it does become depleted does not result in rapid corrosion attack.
Regards Scott.
_______________________________________________________________________________
Scott Fisher [scott@psy.uwa.oz.au] PH: Aus [61] Perth (9) Local (380 3272).
_--_|\ N
Department of Psychology / \ W + E
University of Western Australia. Perth [32S, 116E]--> *_.--._/ S
Nedlands, 6009. PERTH, W.A. v
Joy is a Jaguar XJ6 with a flat battery, a blown oil seal and an unsympathetic
wife, 9km outside of a small remote town, 3:15am on a cold wet winters morning.
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