ENGINE COOLANTS - FAQs
What is Antifreeze?
Most low to moderate temperature coolants and heat transfer fluids use glycols to lower
the freezing point and increase the boiling point of a water-based solution. In common
usage, this is antifreeze; engineers and chemists call these products engine coolants and
heat transfer fluids. There are two glycols in common use: ethylene glycol and propylene
glycol. Both are suitable for use in automotive and heavy-duty engine coolants, and in
aqueous heat transfer fluids. Typically this mixture will contain water, 35-60 % glycol,
and an additive package which includes corrosion inhibitors, anti-foam additives, and
How does antifreeze differ from engine coolant?
Engine coolant is a generic term used to describe fluids that remove heat from an engine
and prevent it from freezing in the winter. There are also antifreeze products intended
only to provide freeze protection for RVs, boats, and idle equipment. These are not
suitable for use in engines or heat transfer systems.
I know that antifreeze prevents my engine’s cooling system from freezing in the
winter; what else does antifreeze do for my engine’s cooling system? Do I need
antifreeze if live in Florida?
Engine coolant increases the boiling point to prevent boil-overs. Plain water boils at 212
°F, a 50% engine coolant solution at 223 °F, and a 15 psi pressure cap increases this to
265 °F, the required mixture for proper engine operation. Modern vehicles are equipped
with light weight radiators and heater cores with very tolerance for corrosion, and modern
engine coolants are formulated to protect them. Using plain water will promote corrosion
and overheating. A 50% glycol engine coolant solution is the minimum amount
recommended by vehicle manufacturers.
How does the cooling system work?
Engine coolant is pumped through the engine where it absorbs heat, through the radiator
where it is cooled, and back to the engine. The fan moves air over the radiator, the hoses
provide flexible connections between the stationary radiator and the vibration of the
engine. The thermostat slows coolant flow until the engine is up to proper operating
temperature. The heater core acts as a second radiator, heating the cabin with engine
waste heat. The expansion tank—where additional coolant is monitored and added as
needed— allows for expansion with temperature changes and seal the system against
oxygen intrusion. It is a team, the coolant protecting the engine from over heating and
corrosion, and the cooling system protecting the coolant from oxygen and excessive heat.
Together, they maintain the engine at its most efficient temperature, whatever the
environmental or operating conditions.
Modern engine run hot to burn clean. Operating temperatures have increased to reduce
exhaust emissions and improve fuel economy. Today’s engines run on the borderline of
overheating, with in-cylinder combustion temperatures around 2,000 °F. As fuel is
burned in the engine, about one-third of the energy in the fuel is converted to kinetic
energy for moving the vehicle, another third goes out the exhaust pipe, and the remaining
third is removed by the cooling system. When no cooling is provided, metal parts warp
and the pistons seize.
How much antifreeze is produced each year?
Worldwide, over 400 million gallons of antifreeze concentrate are sold each year. After
with 50% water, this yields about 800 million gallons of engine coolant. It is estimated
that 50% of this is dumped on the ground and into storm sewers, 45% into sanitary
sewers, and less than 5% is properly recycled.
Most people I know never bother with antifreeze maintenance, yet they change their
oil regularly. Because most engine coolants last so long, is it OK to neglect the
No, it is never OK to neglect cooling system maintenance. Scale buildup and corrosion in
radiators, for example, can cause overheating problems or radiator failure. Changing your
antifreeze regularly will keep your engine running smoothly and help prevent
breakdowns. The American Automobile Association reports that the most common cause
of vehicle roadside breakdowns is cooling system failures.
How often do I need to change my antifreeze?
You should always follow the vehicle or engine manufacturer’s recommendations for
antifreeze change intervals and cooling system maintenance. Suggested intervals range
from 2 year/24,000 miles to 5 years/100,000 miles.
If I replace the antifreeze in my automobile with recycled antifreeze will it void my
cooling system warranty?
The antifreeze formulation must be compatible with and meet the performance
requirements of the vehicle manufacturer. It is not relevant what brand it is or whether it
Under the Magnuson-Moss Warranty Act (15 U.S.C. 2302) and general guidelines of the
Federal Trade Commission, an original equipment manufacturer (OEM) may not make its
vehicle warranty conditional on the use of any specific brand of motor oil, oil filter,
antifreeze, or any other component unless the manufacturer provides it to the customer
free of charge during the warranty period. If an OEM or dealer requires a customer to use
its motor oil, oil filters, or antifreeze, the customer should demand the products be
provided free of charge. If the demand is refused, the customer should ask for a copy of
the warrantor’s approved FTC waiver.
How can I best measure the freeze point of my engine coolant (ethylene or propylene
A refractometer is the most accurate way
to check the percent of antifreeze in
coolant. Hydrometers and floating balltype
testers are sensitive to dirt and can
loose accuracy over time.
How much water should I mix with my antifreeze?
A mixture of one part engine coolant concentrate one part with distilled water will result
in a mixture with a freeze point of –34°F and a boiling point of 265°F (with 15 PSI
pressure cap). Do not use concentrate engine coolant without adding water; it does not
circulate well and can lead to overheating. In extremely cold climates using a 60%
ethylene glycol mixture will give freeze protection to -55 °F. Additional glycol will not
further lower the freeze point. Do not add water to pre-dilute engine coolants.
Distilled water? Can’t I just use tap water?
Tap water contains contaminants that can lead to scaling, corrosion, and cracking of
radiator tubes. The following recommended limits are found in Appendix X1. of ASTM
- Chlorides: 25 ppm
- Sulfate: 50 ppm
- Hardness: 20 ppm
- pH: 5.5-8.5 units
- Iron: 1 ppm
Nearly all tap water supplies greatly exceed these limitations. Pre-dilute coolants are
formulated with deionized water and avoid this problem.
Never use water softened by salt exchange; the salt introduced into the water is very
A great deal of work and expense goes into the formulation of quality antifreeze/engine
coolant. Reputable companies use high quality glycols, deionized or distilled water, and
inhibitors that are certified to be low in contaminants (like chlorides) to blend and make
premium quality finished products. Unfortunately, these efforts are wasted when poor
quality tap water is used to blend coolant.
Hardness: Calcium and Magnesium. At high
temperatures these for scale, and they strip the silicate
from the coolant. Heat transfer rates can be reduced
Chloride and Sulfate. These ions contribute to corrosion
and cracking, even when present at very low levels.
Think in terms of adding road salt to your car.
Mixing errors. Improper dilution of the coolant concentrate is a common problem,
resulting in overheating and corrosion.
Coolant seems to disappear from my system. Where does it go?
It is normal for as much as a pint per year to “disappear” from the system. Minor hose
leaks, pump seal seepage, and even evaporation through the hose wall all contribute.
Greater loss rates implicate a more serious problem: defective radiator cap or defective
coolant recovery system, significant hose and clamp leakage, water pump and/or
thermostat issues, cracked cylinder heads or engine blocks, head gasket problems, and
leaking radiators, heater cores or oil coolers. All of these problems can be intermittent,
only occurring during warm-up, cool-down, or high speed operation.
Why does my coolant foam?
Foam in coolant can result from trapped air in the system, a leak on the suction side of
the water pump, an improperly functioning water pump, or low coolant level in the
coolant recovery tank.
Why has my coolant turned rusty?
Some coolants are orange to begin with. If the coolant is orange but clear, check the
owners manual. Mixing green and red coolant types can result in an unpleasant looking
brown color. If the coolant is cloudy and the change is sudden, it is very likely iron rust
and the most probable causes are either oxygen intrusion or stray current electrolysis.
Oxygen can enter the system through:
- loose hose on the suction side of the water pump
- leaking head gasket
- cracked cylinder head
- water pump seal
- low level in expansion tank
- faulty expansion tank hose routing
Stray current electrolysis can be caused by:
- loose radiator fan ground
- loose ground to engine
- faulty temperature sending unit
Faulty coolant can contribute, but rapid changes generally point to a mechanical cause. If
the mechanical system and hoses are in good shape, there is simply not enough oxygen
(required for iron rusting) to allow rapid and wide spread corrosion.
Types and Applications
Is there a performance difference between ethylene glycol and propylene glycol
Ethylene glycol(C2H6O2) and propylene glycol (C3H8O2) are chemically similar—both
are double alcohols and have very similar chemical and physical properties. Both provide
the excellent corrosion protection properties when formulated with appropriate additives.
Propylene glycol is slightly less effective as a freeze point depressant, but it is very close
(see chart below). Freeze point protection insures a free-flowing solution; burst point
protection insures only against broken pipes and is NOT suitable for vehicle protection.
Propylene glycol based engine coolants are not generally formulated to meet the same
manufacturer requirements as ethylene glycol based products, in part because they are
less common. Do check your owners manual for applicability in all cases.
Can I add propylene glycol based antifreeze to my existing ethylene glycol based
Ethylene glycol and propylene glycol are chemically very similar and can be mixed
without harming the cooling system. However, the additive formulation may be different
than the existing engine coolant. Draining and replacing the engine coolant is best.
Adding propylene glycol to existing ethylene glycol coolant does not make the resulting
mixture significantly less toxic.
Can I top off my radiator filled with green antifreeze with antifreeze of a different
color, if I am low and that is all I can find? Are all engine coolants basically the
same, except for color?
Color does not indicate what kind of corrosion inhibitor formulation is contained in
engine coolant. Review compatibility statement on the label. In general, vehicle and
coolant manufacturers recommend a 10% limit on mixing coolant types. If you need to
add more than 10%, it is recommended that you flush and refill your cooling system.
What is long or extended life engine coolant?
“Long life” or “extended life” antifreeze generally means antifreezes that contain organic
acid inhibitors (OAT) as their primary corrosion inhibitors.
What is hybrid engine coolant?
“Hybrid” engine coolants contain both inorganic and organic corrosion inhibitors. These
were developed to combine the best characteristics or conventional (economical, broad
compatibility, good seal compatibility) and long life (long-life, moderate pH for broad
metal compatibility, extended water pump seal life) engine coolants into one product.
Many OEMs are now migrating from conventional and long-life products to hybrids.
Can I use heavy-duty antifreeze for trucks in my car?
Follow the recommendations of your vehicle’s manufacturer regarding the type of
antifreeze to use. Many heavy duty antifreeze products are “universal” and can be used in
What is the difference between “light duty” antifreeze and “heavy duty” antifreeze?
“Light duty” antifreeze is intended primarily for gasoline-engine passenger car
applications. “Heavy duty” antifreeze is intended for diesel engines in both on- and offhighway
applications. Heavy duty engines are defined as those using wet sleeve liners
instead of bored cast iron blocks; these can be subject to pitting if not provided with
specific anti-corrosion chemistry. The use of “light duty” antifreeze in heavy duty trucks
can cause serious engine damage unless an SCA in proper amount is added to the
What is an SCA? When should I use an SCA?
SCA stands for Supplemental Coolant Additive. Heavy duty diesel engine built with wet
sleeve liners can be subject to liner pitting if not provided with specific anti-corrosion
chemistry. Nitrite is used in combination with other additives, and these additives are
subject to depletion in heavy use. Regular addition of SCAs helps maintain proper
additive concentration between antifreeze changes.
This concern is unique to heavy duty diesel engines with high load factors and does not
apply to light duty applications.
What are the nationally recognized standards or specifications for antifreeze and recycled antifreeze?
Compliance with these standards, as applicable, is required for most vehicle applications.
Engine coolant manufacturers, virgin or recycled, should be able supply evidence of third
party testing. Manufactures perform many of these tests on each batch to insure good
quality control. These standards apply equally to both virgin and recycled products.
These standards are copyrighted and are not available on-line. They may be purchased at
the following links:
Who can run these tests?
Your supplier should run many basic tests in-house. For more complex tests and for third
party verification, the following laboratories are respected in the industry:
The US government buys antifreeze under a CID (Commercial Item Description)
specification. What does this include?
US government specification CID-A-A-52624 covers requirements for ethylene glycol
and propylene glycol antifreeze and allows three different concentrations: 100%, 60%,
and 50%. CID-A-A-52624 requires the antifreeze “to be suitable for use in all
administrative vehicles, construction and material handling vehicles and equipment, and
military ground combat and tactical vehicles and equipment.” The US government
encourages the use of recycled antifreeze. See this link:
What do all the different colors of antifreeze mean? What should I be using? What
is compatible with what?
In years past, most coolants were green, were based on ethylene glycol, and contained,
more or less, the same conventional inorganic additive package. Now coolants are
available in a variety of colors, sometimes to identify important differences and
sometimes to help with marketing. Green in heavy duty trucks generally indicates a
conventional formulation, while orange/red colors indicate nitrited organic formulas.
Automobiles have a variety of green, yellow, orange, and red products, all hybrid or
organic. Although there has been much effort within the standards organizations to
develop standards for color and compatibility, nothing formal exists.
Each manufacturer is responsible for testing their formulations in combination with other
formulations to determine compatibility. Labels and specification sheets should give
some guidance. In general, conventional coolants are compatible with conventional
coolants. Hybrids coolants have broader compatibility and are generally compatible with
other hybrids and with conventional coolants. Organic coolants are generally compatible
with other organic coolants. However, in each case it is probable that the life of the
coolant will have been shortened from an extended drain interval to a 2 year/24,000 mile
interval. Draining and refilling with fresh coolant of a type similar to factory fill is best.
Toxicity and the Environment
I have seen propylene glycol based antifreeze sold as an environmentally friendly
alternative to ethylene glycol based antifreeze. Is this true?
Both propylene glycol and ethylene glycol are biodegradable and will soon break down
into carbon dioxide and water. Neither should be dumped in the environment as they
contribute to water pollution, contain chemical additives, and have been contaminated
with trace metals and oil in use. Both ethylene glycol and propylene glycol coolants
should be returned to a recycling center to minimize harmful effects on our environment
after use. Spills should be cleaned up immediately.
The toxicity of both ethylene glycol and propylene glycol to fresh water and marine
organisms are low and very similar. The primary impact of glycols on surface water are
to reduce the oxygen content of the water due to microbial activity.
See the below link for a discussion of human and environmental toxicity:
Is used antifreeze poisonous?
Yes. Glycols have a sweet taste that small children and animals can find attractive. As
stated, ethylene glycol is significantly toxic to humans. If ingested, antifreeze affects the
central nervous system, can lead to kidney failure, and can cause death. Symptoms of
antifreeze poisoning include vomiting, weakness, and loss of coordination. Contact your
local poison control center for first aid information.
Several States require the addition of a bittering agent to make antifreeze less tasty to
children and animals; however, this is not proven to prevent ingestion. Every year about
10,000 cats and dogs are victims of accidental poisoning by ingestion of antifreeze.
Always keep antifreeze securely stored to protect yourself and others.
The following link to the CDC provides additional information:
Does improper disposal of used antifreeze endanger the environment? I can’t just
dump it down the storm drain or in the sewer?
Dumping a chemical wastes into surface water via a storm drain is a violation of the
Clean Water Act. Dumping of the used antifreeze into the sanitary sewer is regulated by
the local authority and is illegal in most jurisdictions. Even small amounts can contribute
to water pollution in small streams; spent coolants contain additives, engine
contamination, and 3000 times the biological oxygen demand of raw sewage.
Similarly, commercial quantities can cause up-set conditions at the sewage treatment
How can I protect the environment and myself from used engine coolant? What
about used antifreeze from my RV or boat?
Store used engine coolant in a leak-proof container with a secure lid. Dispose of the
coolant at an appropriate collection center or call an engine coolant recycling company
for collection and re-manufacture into a usable product. Most engine coolant recyclers
market products back to the commercial and industrial trade.
RV and marine antifreeze are generally recyclable along with used engine coolants, as
long as the glycol concentration is greater than 30%. Check with your recycler.