Product Bulletin: 2009/01
About Coolant/Antifreeze
C.S. Chua, Technical Director Peregrine-Pacific
Have you ever wondered why some automotive coolants are green, while others are blue,
pink, orange or a variety of colours other than the conventional fluorescent green? Which is
better and which is the right type for your vehicle? The answers lie in knowing the types of
coolant you are using and having some understanding of your vehicles.
Automotive coolant is an important component for the overall maintenance of the vehicle,
but has constantly been overlooked. It plays a critical role in sustaining engine heat balance
by removing excess heat generated during the combustion process. In a heavy-duty diesel
engine, only one-third of the total energy produced is used to propel the vehicle forward. An
additional one-third is removed as heat from the exhaust system (ahh… that’s why car has
exhaust system!). Bulk of the remaining one-third of heat energy is taken away by the coolant.
Overheating will result in accelerated deterioration of the engine oil and subsequently, the
engine itself.
HISTORY AND DEVELOPMENT OF COOLANTS
Automotive coolant used to be very simple. Every 2 years or so, just drain out the old coolant
and replace with new one. I have known drivers who just topped up regularly with tap water
without any major problems. While water provides excellent heat transfer properties, glycol
(the main ingredient in all types of coolant), provides additional freeze protection which is
critical in cooler climate applications.
More importantly, a properly formulated
coolant/antifreeze will also contain appropriate amounts of rust and corrosion inhibitors,
antifoam agents and other additives for the protection of the cooling system. While these
ingredients constitute only a small fraction of the overall coolant, they differentiate one
coolant from another.
Picture courtesy of Machinery
Lubrication
Historically (at least until 1994) in North America, automotive coolants
had been green in colour.
These coolants typically use a
phosphate/silicate mix and/or borate in their corrosion protection
formula. Conventional inhibitors (inorganic oxides such as phosphates,
silicates and borates) work by forming a protective blanket over the
metal parts in the system.
This is called the Inorganic Additive
Technology (IAT). As these inhibitors are depleted while forming the
protective layer, conventional green IAT coolants need to be changed
at regular intervals, typically every 2 years.
The conventional green coolant generally works well for most engines.
However, over time, demands for more lasting coolant (because people neglected to
change every two years) and diverse geographical conditions and preferences, resulted in
the development of new coolant technologies. In the European market, it was discovered
that minerals (calcium and magnesium) in the harder water, reacted with the phosphate
inhibitors to form calcium or magnesium phosphates. These could lead to scale formation on
hot engine surfaces, resulting in a loss of heat transfer and corrosion underneath the scale. It
forced the development of phosphate-free coolants.
In Asia, a different kind of problem exists. Apparently, silicate drop outs
and abrasiveness have led to damages in water pump seals and poor
heat transfer. Silicates do have their strength, in that they offer instant
protection to the cooling system. Many conventional green coolants
contain silicates, which provide a high level of fast acting protection
Silicate build-ups
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Product Bulletin: 2009/01
About Coolant/Antifreeze
C.S. Chua, Technical Director Peregrine-Pacific
against corrosion and pitting in the cooling system. Unfortunately, silicates do have a lifespan
of about 2 years. If left longer in the system, silicates build up in the radiators and heaters,
causing overheating and also poor heater performance. Silicate drop outs occur after the
coolant is “spent”, and the inhibitors drop out of the solution. Once silicates drop out of the
coolant, metal corrosion is no longer suppressed, and the components begin to deteriorate.
Silicate-inhibited coolants are banned by some Asian automotive Original Equipment
Manufacturers (OEMs).
Organic Acid Technology (OAT) gives rise to a range of new Extended Life Antifreeze Coolant
(commonly referred to as ELC or sometimes, XLC). It contains neutralised organic acids
(organic acid salts) that protect engine parts from corrosion. OAT includes ingredients such as
sebacate, 2-ethylhexanoic acid (2-EHA) and other organic acids but no phosphates or
silicates.
Organic inhibitors do not deplete as quickly as the inorganic inhibitors of
conventional coolants, and properly formulated OAT coolant can claim extended life of up to
5 years or 150,000 miles (240,000 km). OAT coolant provides excellent long term protection for
cast iron and aluminium, but may not be the best choice for older cooling systems with
copper/brass radiator or heater cores, especially those with lead solders. This is because OAT
fluids may not protect quickly enough in fast corrosion conditions like boiling, and also may not
protect solders. This may make some OAT coolant not backward compatible with older green
conventional coolant engines. However, all these depend on the actual formulation of the
OAT coolant. Extended-life carboxylate-based coolants were developed to be globally
accepted and provide superior performance over existing technologies. Full carboxylate
coolants contain no silicates and thus meet the stringent Asian specifications. At the same
time, they also meet the European requirements because of zero phosphate content. The
new universal coolants use unique OAT-based corrosion packages with proprietary organic
acids such as carboxylate, to provide a broad spectrum of protections.
Carboxylate inhibitors provide corrosion protection
By chemically interacting with the metal surfaces
where needed and not by coating insulating layers
as is the case with conventional and hybrid types.
The implications of this functional difference are
enormous; extended life cycles, unsurpassed high
temperature aluminium protection and heat transfer advantages. High quality carboxylate - based
OAT coolants have demonstrated performance of
more than 32,000 hrs in stationary engine applications without the need for a change of coolant.
These products have developed international popularity due to the unsurpassed corrosion protection
for extended time intervals.
Picture courtesy of Machinery Lubrication
Original water pump from Caterpillar engine after more than
750,000 miles using Extended-Life Coolant (ELC)
To replace phosphates, European coolants use a mix of inorganic oxides (like silicates) and
inhibitors such as carboyxlates (organic). This is termed the Hybrid OAT (HOAT) coolant
because of the combination of the conventional inorganic technology with a fully
carboxylate or organic technology. The idea with hybrids is to provide quick acting all-round
protection and extended drain intervals. Hybrid coolants generally can replace conventional
green coolant in older vehicles.
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Product Bulletin: 2009/01
About Coolant/Antifreeze
C.S. Chua, Technical Director Peregrine-Pacific
In addition, while the European OEMs (BMW, VW, etc.) shunned phosphates, the Japanese
(Honda, Toyota) believed that they work better than borates, which may be bad for
aluminium components. Some of the Japanese OEMs in fact specify mixtures high in
phosphates and low in borates/silicates due to the fear that lack of maintenance may cause
borate corrosion. In general, European manufacturers implemented long life coolants with
either hybrid (BMW, Mercedes, Volvo) or OAT (Opel, Ford Europe, VW) technologies. The
major Asian manufacturers have mainly adopted OAT types as extended drain fluids.
COLOURS OF COOLANT
If there are only three types of coolant technologies (IAT, OAT and HOAT), why are there so
many different colours of coolant? This is basically a marketing decision. When the market
started to move away from the traditional green coolant, manufacturers also started selling
proprietary formulas in a variety of colours. European coolants exist in various colours; typically
each manufacturer requires a different colour. Similarly, the trend continues in Asia. Though
colour itself has no bearing on the quality of the coolant, it does serve some practical
purposes, beside the obvious marketing value.
The chart below shows some known coolant types and colours:
Colour
Manufacturer
Green
Shell &
Texaco
Prestone
Yellow
Green
Orange
Amber
Orange
Pink
Blue
Yellow
Red
Yellow
Pink
Yellow
Bardahl
- GlyCool
Bardahl
- GlyCool ELC
Peak
Global
LifeTime
GM
- Dex-Cool
VW
-G12
BMW
Conventional
(IAT)
Conventional
Long Life
OAT
HOAT
Silicate and
amine-free
EHA + extra
Carboxylate
2-EHA
Mercedes
- G-05
Chrysler
> 2001
Ford
- G-05
Toyota
Valvoline
- Zerex G-05
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Product Bulletin: 2009/01
About Coolant/Antifreeze
C.S. Chua, Technical Director Peregrine-Pacific
As far as colour is concerned, manufacturers are concerned with the following issues:
1. The ability to identify their approved fluids in the workshops.
2. The ability to discern the coolant level in expansion bottles that may have turned
yellow with time.
3. The lifetime colour durability of the coolant as well as consideration of other underhood fluids to avoid contamination. For example, adding a red colour coolant into the
brake system as a DOT 3 brake fluid could have catastrophic consequences.
CHECKING THE COOLANT
The market is filled with so many different types, brands and colours of coolant, that it is almost
impossible to distinguish one from another just by the appearance. Colour is not a good
indicator of the quality of a coolant. The best practice is to know and use the exact coolant
required for your engines. If appearance itself is difficult to differentiate coolants, what else
can we do? One solution is to buy from reputable sources of genuine products. The other is to
do your own testing wherever possible. Checking coolant is actually simpler than most people
thought.
One of the most important checks on a coolant is the glycol to water ratio. Most engines
recommend a 50/50
mix of ethylene glycol and water. In some
circumstances, industrial
engines may utilize other base fluids such as additized water or a mixture
of propylene glycol and water. Although many
techniques are
available, the refractometer offers the most
reliable method to
identify the precise glycol content of the coolant.
Atago handheld
refractometer
Another simple and yet important test that should be carried out
Regularly on coolant is the pH value. The pH scale runs from 1 to
14. Distilled water is neutral and has a pH value of 7. Aluminium
and zinc oxides are both soluble in alkali solutions. So, if the coolant’s pH is allowed to drop too much below neutral (becomes
acidic) or move far above pH 7 (becomes alkali), increased corrosion activity of metals can be expected. Some coolant technologies can protect at as low as pH 6.5, however, it is typically
not a good practice to allow a coolant to operate below a pH
value of 7.
Image courtesy of Jon’s Images Inc.
The coolant level is checked through the
Other recommended checks are
really just common sense routines.
Coolant level and all the cooling
system components should be
regularly inspected. Coolant level
should be checked with the car
Picture courtesy of UMR Engines
hood up. Overheating problems
Checking pH of coolant by simply matching
the paper test strip against a standard colour
may be caused by a low coolant
scale
level. There are two lines on the
recovery reservoir. The higher line
is typically marked “hot” or “maximum”. The lower line is usually
marked as “minimum” or “cold”. As the coolant warms up, the
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Product Bulletin: 2009/01
About Coolant/Antifreeze
C.S. Chua, Technical Director Peregrine-Pacific
liquid expands causing the level of coolant to move up. Use the top “maximum” or “hot” line
as the guide when the engine is hot. If the engine is cold, the lower “minimum” or “cold” line
should be followed. The coolant level should not drop too much below the minimum level in a
properly operating cooling system. Check the system for leaks if the coolant reservoir level falls
below the minimum line. Use the recommended type of coolant to bring the level up to the
correct mark if necessary.
Radiator hoses carry the coolant to and from the engine. A rupture on anyone of the hoses
will result in very quick losses of the coolant. Hoses should be checked so that they can be
replaced before any major problem arises. This should be done while the engine is cold
and the hoses can be touched safely. Inspect each closely, including the underside of the
bottom hose. Squeeze each hose with the hand to check on its hardness. Old hoses can
become so stiff and brittle that vibration can cause them to break. Check hoses carefully for
signs of hardening or cracking. Even a small crack can soon cause trouble. Swollen or soft
hoses indicate that the material has begun to deteriorate. Any of these conditions warrants
replacement.
Squeezing the radiator hose to inspect its hardness
Images courtesy of Jon’s Images, Inc.
Radiator hose problems
Overheating can also be caused by factors other than low coolant level. The radiator may be
blocked, the thermostat is malfunctioning, faulty fan or a failed water pump. If overheating
occurred while the coolant still remains at the proper level, it is usually time to visit a mechanic.
Using a high-quality coolant from a reputable supplier and following careful preventive
maintenance practices will ensure the proper protection of the engine.
SUMMARY NOTES
Lots of misinformation about the compatibility of the different types of coolant technologies
exist in literature and the market place. While it is no good maintenance practice to mix two
different coolants, it will not generally result in compatibility issues as long as high-quality
coolants from reputable suppliers are used. Coolants are generally considered as compatible.
However, mixing coolants of two different qualities results in a mixture of intermediate quality.
While not a disaster, mixing a high-quality coolant with a mediocre one will compromise the
performance of a great coolant. Over-dilution with water would have a negative effect
because the corrosion inhibitors would be at a lower quantities than originally designed.
Coolants are designed to work over a range of dilutions. The optimum for most cooling
systems is 50 percent coolant and 50 percent good-quality water.
References:
Paul Fritz, Chevron Products Company, “Learning Coolant Fundamentals”. Machinery Lubrication. January 2006
Jon Anderson, Jon Images, Inc. “Easy Car Maintenance”
SAE – Society of Automotive Engineers; J-1203 and J-1034
ASTM - American Society for Testing and Materials, D-4985 Engine Coolants Testing
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