Coolant 101


Antifreeze / Coolant Description:
Antifreeze/coolant serves four purposes in a vehicle cooling system.

1.      To lower the freezing point below 32º F / 0º C. (To help prevent freeze up)
2.      To raise the boiling point above 212º F / 100º C. (To help prevent boil over)
3.      To protect the cooling system against corrosion.
4.      To lubricate water pump seals.



Types of Coolant / Antifreeze:

In today’s day and age, there are many variations of coolant/antifreeze and can be quite confusing. But they are all based on ethylene glycol (EG) or propylene glycol (PG). From this, six groups come out. Colors vary from types, to the different manufacturers.

1. Inorganic Acid Technology (IAT) – This is the old typical green antifreeze/coolant that contained Silicates, Phosphates and/or Borates. The average life of IAT was from: 2 years/30,000 miles to about 3 years/36,000miles (dependent on manufacturer’s interval specs).

2. Organic Acid Technology (OAT) – This variation does not contain silicates or phosphates. A version of this is called Dex-Cool that has been used in GM cars since 1996, and Volkswagen/Audi uses a similar version called G12, G12+ and G12++ of this antifreeze/coolant. They contain 2-EHA and /or Sebacate for corrosion protection. This is a long life coolant with an interval of around 5 years/50,000 miles (dependent on manufacturer’s interval specs).
3. Hybrid Organic Acid Technology (HOAT) – Is a combination of organic acid technology (OAT) with a low dose of silicates or phosphates. Most antifreeze/coolant is of this variation. This is a long life coolant with an interval of around 5 years/50,000 miles (dependent on manufacturer’s interval specs).
4. Nitrited Organic Acid Technology (NOAT) – Is an organic acid technology (OAT) that has no silicates or phosphates. It contains nitrates and/or molybdenum as part of their inhibitor package. This coolant is an extended life coolant and does not require supplements. This extended life coolant has a service interval of around 8 years / 750,000 miles (dependent on manufacturer’s interval specs).
5. Nitrited Molybdate Organic Technology (NMOAT) – This coolant is similar to NOAT that has nitrates, but also has Molybdate for diesel wet sleeve liner protection.
6. Poly Organic Acid Technology (POAT) – This a long life coolant that is propylene glycol based, organic acid technology. Currently Amsoil is the only manufacturer for this coolant.




Antifreeze vs. Coolant

Antifreeze – Is undiluted and must mixed to a 50/50 antifreeze to water ratio. Distilled water should be used to dilute antifreeze. Use the correct ratio recommended by vehicle manufacturer. As a note, running straight antifreeze in an engine, will result in a hotter running engine. Antifreeze does not have the heat transferring abilities as water.


Coolant – Is pre-diluted and ready to use. Coolant does not require water to be added


SCA (Supplemental Coolant Additive) / DCA (Diesel Coolant Additive) – Because additives in conventional (IAT) and hybrid organic acid (HOAT) coolants are consumed during the vehicle’s operation, they must be refortified with supplemental coolant additives (SCA/DCA) in order to maintain effective corrosion protection. On the other hand, OAT and NOAT coolants do not require SCAs. Also note that the inhibitor package does not determine the level of freeze or boil over protection; the inhibitor is responsible for corrosion protection only.





⇒Most antifreeze / coolants are dangerous to humans and animals if ingested. They can cause severe injury or death. Use caution with children and animals since most coolants are sweet tasting.
⇒Dispose of used antifreeze / coolant to proper recycling center.
⇒Wear personal protective equipment.
⇒Use caution when working with hot coolant.





Acidic (pH) – Liquid having a pH rating of 1 – 6 on the pH scale (sour). Acids fall in this scale.
Alkaline (pH) – Liquid having a pH rating of 8 – 14 on the pH scale (sweet). Caustics fall in this scale.
Antifreeze – This type is 100% antifreeze and has to be diluted with water to achieve desired freeze point. Running 100% antifreeze is not advisable.
Basic (pH) – see Alkaline.
Benzoate – A corrosion inhibitor that is the main inhibitor in HOAT antifreeze/coolant and G-05 antifreeze/coolant.
Benzotriazole (BZT) – An inhibitor that protects brass and copper against corrosion.
Boiling Point – The temperature that a liquid changes from liquid to gas.
Borate – A chemical used in antifreeze/coolant SCAs to maintain the pH as it ages. It is a pH buffer.
Carboxylates – Organic acid anti rust inhibitors.
Caustic – A solution that has a pH of 12 to 14 pH.
Cavitation – The formation of bubbles and the immediate implosion of them. This produces a shock wave that causes pitting and erosion where it is occurring inside the cooling system.
Coolant – This type comes pre-mixed with water in a 50/50 mix. It is ready to be used and should not be diluted with water.
Coolant System Flush – A chemical or water cleaning of a cooling system to remove old antifreeze/coolant and particles from a cooling system.
Colligative Agent – Antifreeze/coolant is a colligative agent that raises and lowers the boiling point and freezing point in a cooling system.
Convective Heat Transfer – Heat transfer thru fluid movement in liquid or gas. Cooling systems work in this manner.
Corrosion – A destructive reaction of a metal with another material, e.g. oxygen, water, chemical (either acidic or alkaline).
Corrosive – A chemical (liquid, solid, or gas) that can cause destructive damage to body tissues, metals and other materials.
Deionized water (DI) – see Distilled water.
Denatonium – A bitter tasting agent added to antifreeze/coolant to make it bitter.
Distilled water – Water that has had minerals ions removed. In a cooling system, hard water contains calcium and magnesium that will form deposits in a cooling system.
Electrolysis – A chemical process that induces the transfer of metal by way of electrical current flow.
Ethylene Glycol – A colorless, odorless, syrupy, sweet alcohol that is toxic
Hybrid Inorganic Acid Technology – Antifreeze/coolant that is either ethylene glycol or propylene glycol that has a low dose of silicates or phosphates added.
Freezing Point – The temperature that a liquid changes from liquid to solid.
Galvanic Corrosion – This happens when dissimilar metals are in electrical contact. The Anode (+) metal will corrode faster than the Cathode (-) metal.
Glycerol – It was used as antifreeze/coolant before it was replaced by ethylene glycol.
Hybrid Organic Acid Technology (HOAT) – Antifreeze/coolant that is either ethylene glycol or propylene glycol that has a low dose of either silicates or phosphates.
Hydrometer – Measures the density of the coolant to the density of water. Reads freezing point and boiling point of antifreeze/coolant.
Inorganic Acid Technology (IAT) – Antifreeze/coolant that is either ethylene glycol or propylene glycol that has silicates and phosphates added (traditional green).
Ion – Is an atom or a molecule in which the total number of electrons is not equal to the number of protons, giving it a net positive or negative charge.
Molybdate – An additive to prevent cylinder liner cavitation.
Neutral – Having a pH of 7. The middle of the pH scale.
Nitrate – An anti-corrosion additive in preventing rust.
Nitrite – An additive to prevent cylinder liner cavitation.
pH – Potential for hydrogen.
pH Scale – A scale of 1-14, 1-6 being acidic, 8-14 being alkaline, and 7 being neutral.
Phosphates – An inorganic chemical that insulates the metal in a cooling system against corrosion.
Plasticizer – A substance that softens certain plastics, silicones, and nylons.
Propylene Glycol – Similar to Ethylene glycol but not as sweet tasting, but is not as toxic to environment.
Organic Acid Technology – Antifreeze/coolant that is either ethylene glycol or propylene glycol that has no silicates and phosphates added (Dex-cool and VW/Audi coolants).
Refractometer – An instrument that measures the refractive index of a liquid.
Reserve Alkalinity – A coolants ability to neutralize acid.
Sebacate – An organic acid added to coolant for corrosion protection.
Silicates/Silicone – An additive to antifreeze/coolant that reacts with the metals in a cooling system to protect against corrosion, particularly with aluminum. It is based from sand and has deemed abrasive to coolant systems and certain water pump seals.
Sodium Hydroxide – An additive to help maintain pH balance.
Sodium Silicate – Used in block sealers, head gasket sealers, and radiator sealers. Called liquid glass that forms a powerful sealant.
Surface Tension – Is the property of the surface of a liquid that allows it to resist an external force.
Surfactant – Is a compound that lowers the surface tension of antifreeze/coolant and allows better heat transfer. Used in additives designed to help lower cooling system temps.
Triazole / Thiazoles – An additive for corrosion protection, particularly with brass and copper.
Tolyltriazole (TTZ) – An inhibitor that protects brass and copper against corrosion.
2-EHA (2-ethylhexanoic acid) – An organic acid added to coolant for corrosion protection. It is a plasticizer that can damage silicone rubber gaskets and certain nylon gaskets.





ASTM – American Society of Testing and Materials
ATC – Automatic Temperature Compensated
DCA – Diesel Coolant Additive
DI – deionization
DMM – Digital Multi Meter
DVOM – Digital Volt Ohm Meter
EG – Ethylene Glycol
ELC – Extended Life Coolant
ESI – Extended Service Interval
HOAT – Hybrid Inorganic Acid Technology
IAT – Inorganic Acid technology
LLC – Long Life Coolant
NORA – National Oil Recyclers Association 

NPG – Non-Aqueous Propylene Glycol
OAT – Organic Acid Technology
PG – Propylene Glycol
pH – potential for hydrogen
SCA – supplemental coolant additive





Antifreeze/Coolant Pros and Cons:


⇒Lowers freeze point
⇒Raises boiling point
⇒Lubricates water pump
⇒Prevents corrosion


⇒Does not have a good heat transfer compared to water
⇒Harmful to environment if improperly disposed
⇒Mixing of two different antifreeze/coolants can damage a cooling system
⇒Antifreeze/coolant not replaced at service intervals can damage a cooling system
⇒Improper antifreeze to water ratio mix can affect desired protection and will affect corrosion protection, freeze point and boiling point.





Antifreeze/Coolant Checks:

If you follow four simple rules, you can prevent antifreeze/coolant problems.

⇒Use the manufacturers recommended type for the vehicle.
⇒Replace at manufactures recommended intervals or add SCA / DCA. *
⇒Never mix different antifreeze/coolant types.
⇒Perform antifreeze/coolant checks at service intervals (at oil changes).


* Note: When using antifreeze, it has to be mixed with water to achieve the desired freeze point protection. Never use tap water; it contains minerals, silica, chlorine and fluoride, all of which can leave deposits in the cooling system.  This is why only distilled water should be used. Coolant should not be diluted with water, it comes pre-mixed 50/50 and is ready to be used.



Antifreeze/Coolant Tests: The following tests will check to see if the freeze point (antifreeze to water ratio) is correct, pH and reserve alkalinity are in specs for corrosion protection, and check for unwanted current in the cooling system that could lead to electrolysis damage. The tests are fairly simple, but they require test tools to perform checks. In some cases more than one test must be performed on a cooling system, more so if the system has been having problems.


1. Coolant Test Strips – By far the easiest test to perform. They check for pH level (corrosion protection), reserve alkalinity, sulfates, nitrates, chlorine and freeze point/ boiling point. When purchasing test strips, make sure they are compatible with antifreeze/coolant in cooling system. Also, they are variances in testing from manufacturer to manufacturer of the strips. If using SCA/DCA, test strips will determine how much to add or if antifreeze/ coolant needs replacing. Follow the instructions to achieve accurate test results. The strip is dipped into antifreeze/coolant and colors on strip are compared to the chart on the kit.

Coolant antifreeze test strips
Coolant Strips and Color Examples

⇒Easy to use

⇒Low price
⇒Fast results



⇒Must be used at specific temperatures or readings must be temperature compensated.
⇒Have a shelf life (expiration date)
⇒Won’t work for color blind people
⇒Correct strips must be used for particular cooling system being checked.


2. Hydrometer – Measures the gravity density of antifreeze/coolant. They convert a specific gravity measurement into a freeze point level.  Hydrometers are made of a container (glass or plastic) that are designed to draw in the sample fluid. Inside the sample chamber there is a float that contains a ballast weight made of either pellets, disks, floating balls or an arrow. The chamber has a scale and where the ballast floats to the corresponding scale the reading is taken. Hydrometers are accurate only with ethylene glycol antifreeze/coolant and will not work with propylene glycol antifreeze/coolant.

Hydrometer tester
Hydrometer Tester


⇒Low price
⇒Fast results
⇒Easy to use

⇒Must be used at specific temperatures or readings must be temperature compensated.
⇒Will not work with propylene glycol antifreeze/coolant (not accurate).
⇒Air bubbles in sample fluid will affect reading.
⇒Friction of ballast in test chamber will affect reading.
⇒Not very accurate, can be off plus or minus 8 degrees.
⇒Quality of tester can cause skewed readings.


3. Refractometers – Is a precision optical device capable of very accurate specific gravity readings for antifreeze/coolant, battery electrolyte, and windshield washer fluid. It is an optical tool, in which a sample of the fluid is placed on the test window in the refractometer body.  The sample is viewed thru the eyepiece, and where the reading intersects the scale the reading is measurement. The measurements are based on the “Refractive Index” in the way light passes thru the fluid. There are more modern units which are digital refractometers and are fully electronic. The units are also automatically temperature compensated (ATC) and temperature is factored into the reading. Again, as in any tool, follow the manufacturer’s instructions to achieve an accurate reading.

refractometer antifreeze coolant
Refractometer Showing Viewing Scale


⇒Very accurate
⇒Models can measure antifreeze/coolant, battery electrolyte, and windshield washer.
⇒Automatically temperature compensated (ATC).


⇒More expensive than hydrometer and test strips.
⇒Can be hard to read.


4. DMM (Digital Multi Meter) – Can be used to check current in a coolant system. Too much current in a cooling system can cause electrolysis and damage cooling system components. Current is generated under two conditions:
The antifreeze/coolant has been in the cooling system way past its service interval. As coolant ages, the additives in the antifreeze/coolant that keep it neutralized become depleted, over time the coolant starts to develop an electrical charge from passing over dissimilar metals. It starts acting like a battery and the electric current produced starts removing metal from the engine surfaces. This is called electrolysis and it affects aluminum components in particular.

⇒The other type of current produced in a cooling system is caused by bad electrical grounds. This causes current to flow back to the battery thru the cooling system. This will also damage metal components in a cooling system. Assuring all ground points are clean and secure will eliminate this problem.

The following is the procedure for testing a cooling system with a DMM:

Note: Use personal protective equipment, and use caution with running engines.

A)   Remove radiator or reservoir cap.
B)    Insert red DMM lead into radiator (do not let the lead touch the radiator or reservoir) and black lead to negative post of battery.
C)    If reading of DMM is .3 Volts (300mV) without engine running, then the anti-freeze is holding a charge and should be replaced.

Start the engine and read DMM readings. Interpret readings below:

Caution: Use caution when working on a hot and/or pressurized cooling system. Make sure all pressure is relieved from cooling system before removing coolant reservoir or radiator cap. 


DVOM DMM Coolant Antifreeze Testing
DMM Coolant Antifreeze Testing

Interpreting Results:

⇒ Below .1 Volts (100mV) = Cooling system is OK.

⇒ .1 Volts (100mV) to .2 Volts (200mV) = Cooling system is starting to have too much current flow, Antifreeze/coolant should be replaced or grounds should be checked.

⇒ .2 Volts (200mV) to .3 Volts (300mV) = Too much current flow thru cooling system, potential for electrolysis. Antifreeze/coolant should be replaced or grounds should be checked.


If readings are above .3 Volts (300mV) with the engine running, this could be caused by bad grounds and the cooling system is being used to transfer ground. To check to see if bad grounds are the cause of the high voltage using the DMM. Connect the DMM, as previously shown.

A)   With the DMM connected, crank the engine and observe DMM reading. If readings show big voltage spike, then bad grounds are probably the problem.

B)    With the engine running at high RPM of 1,500-2,000RPM and all loads of off, observe the voltage reading. Then turn on all vehicle loads and observe DMM with engine still at high RPM. If voltage readings increase, then bad grounds are probably the problem.


Note: If voltage readings do not fluctuate, then coolant is problem.


If voltage is detected in cooling system, then you have to determine if current is coming from the antifreeze/coolant itself or from a bad ground. Test as Follows:

a)    With DMM connected in the above figure, remove the +positive cable from the battery and observe DMM voltage reading.

b)    If voltage reading did not change, then voltage is coming from the antifreeze/coolant itself. Replace antifreeze/coolant and re-check test.

c)    If voltage reading disappears after removing +positive battery cable, then the problem is bad grounds. Check and clean all ground connections. Re-check system to ensure current has dissipated to a safe level. In extreme cases, supplemental grounds may have to be installed.



⇒Test strips, hydrometers, and refractometers don’t check for current in systems.


⇒If low end (cheap) DMM is used, readings could be skewed.
⇒If cooling system is pressurized, test cannot be performed.



Preventative Products:

There are many products available to supplement a cooling system from preventative and repair. But beware of the use of these products; research the product before pouring it into your cooling system. Like the saying goes, the remedy maybe worse than the problem. Some of the products available are:

Stop leak – Stops radiator, head gasket, and block leaks.
Electrolysis Eliminator – additives that eliminate and prevent electrolysis.
Anode Inserts – It is a drop in element or is part of the radiator cap. It is a piece of metal that is sacrificial; the electrolysis will attack the anode piece instead of the cooling system.
SCA – Supplemental Coolant Additive, additives that maintain and fortify the antifreeze/coolants anticorrosive and freeze properties.
Coolant Filters – Used to filter and remove particles from cooling system. Some filters release SCA’s into the cooling system to maintain system.
DCA – Diesel Coolant Additive, see SCA.
Extra Grounds – In a vehicle with various supplemental electrical add-ons, extra grounds help get the current back to battery, rather than thru the cooling system.
Temperature Reducing Products – These products (Surfactants) promote better heat transfer by reducing the surface tension between the antifreeze/coolant and the cooling passages of the engine.



Coolant Types and Colors:

Antifreeze/coolant in natural form is colorless; manufacturers add color to help identify it. The problem is that different manufacturers are using similar colors for totally different antifreeze/coolant configurations. Be careful not mix antifreeze/coolant; this can cause serious cooling system problems. If in doubt of what is in the cooling system, completely flush out cooling system (this may require three or more flushes with water). This will help in not mixing the old antifreeze/coolant with the new and establish a good baseline for maintenance.


Why different antifreeze/coolant types? In Europe, they use phosphate free antifreeze/coolant. The hard water in Europe contains calcium and magnesium. When mixed with the phosphate, they form calcium or magnesium phosphate, which leads to scale build up in the cooling system. They use a relative low dose of silicates for corrosion protection. On the other hand Asians don’t use silicates because they deem it abrasive to water pump seals. They use a low dose of phosphates for corrosion protection. GM uses Dex-Cool since 1996 which doesn’t use either phosphate or silicates. It contains Sebacate and 2-EHA for corrosion inhibitors. Dex-Cool is also involved in a big controversy about damaging cooling systems. And the list of different antifreeze/coolant grows as manufacturers expand the types. The goal of all new antifreeze/coolant is for long life and intervals are slowly increasing more and more. Of all the colors of antifreeze/coolant, the color you don’t want to see is brown. Brown indicates contaminated, mixed antifreeze/coolant or rust in the system. A system with this problem requires immediate attention to avoid serious damage. For best results follow manufacturers recommended antifreeze/coolant for the vehicle.


Universal Antifreeze/Coolants: Aftermarket antifreeze/coolant makers are marketing Universal coolant that is compatible with all makes and types of antifreeze/coolant. They are OAT (Organic Acid Technology) that doesn’t have silicates or phosphate, they contain proprietary corrosion inhibitors. Some claim that they are lifetime, but again checking coolant at service intervals to make sure it is in specs. Again, before pouring anything into your cooling system, do some research on the product.  Make sure it is compatible with your cooling system.


Waterless Coolant: This type of coolant uses no water in its composition. Since no water is used, it has a higher boiling point, a lower freezing point and there is no corrosion since there is no water. Also since no water is used, there is no pressure build up with heat. It contains no silicates or phosphates. While this technology is not new, it is worth doing research for the vehicle or application it will be used on. Response on how the product works is mixed, from great to bad.



⇒Better heat transfer since no water to create hot spots or cavitation.
⇒Waterless coolant boils at 375º F (191º C), while coolant mix of 50/50 boils at 263º F (128º C).
⇒Waterless coolant freezes at -40º F (-40º C), while coolant mix of 50/50 at freezes at -34º F
(-37º C).
⇒Conventional antifreeze requires a radiator / reservoir cap of about 15psi. to pressurize system to raise boiling point. Waterless coolant requires a 1 to 2 psi. cap, since there is no water, little pressure is produced.
⇒Since little pressure is generated in the cooling system, less stress is exerted on cooling system hoses, gaskets, O-rings, radiator, heater core, and water pump.
⇒With little pressure on the cooling system, leaks are less susceptible.
⇒It inhibits corrosion, since no water is used.
⇒With better heat transfer there is less load on electric fans or mechanical fans.
⇒Environmentally safe, since waterless coolant is propylene glycol (PG) which non-toxic to humans, animals and plants. While most conventional antifreezes are ethelyne glycol (EG) are toxic and have a sweet taste.




⇒If the vehicle has a coolant leak, it must replenished with waterless coolant. This can be a problem if it is a huge leak and waterless coolant is not available. If water or regular coolant is used, the waterless coolant will lose all of its benefits and have to be flushed.
⇒Before adding waterless coolant to a vehicle cooling system, it must be flushed with a special flush agent to remove any water and old coolant.
⇒Waterless coolant is more expensive that conventional coolant. It is two to three times more expensive.
⇒Waterless coolant is not readily available at most parts store. Purchasing coolant will most likely have be done from an online vendor.
⇒Currently one manufacturer produces waterless coolant.
⇒It would be recommended to always carry extra waterless coolant in case of leaks.
⇒In some applications, hotter engine operating temperatures have been reported.
⇒Has a higher viscosity than conventional antifreeze/coolants, putting more load on water pump and engine.



Resource Links:

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2 Comments on “Coolant 101

  1. Outstanding, you guys leave nothing for any mechanic to wonder what else could he learn to understand the coolant concept, there’s nothing about too little information, again you taken training to a complete outer level. I found myself taking some of your info to update my own training presentations, it will be very hard for me to have a different point of view or even add information to a complete training curriculum.
    thank you guys and keep up the good work, I take pride knowing that I had something to do on your quest for excellence that you have achieved.

    1. Thank you again Luis. We learned a lot from your instructor days here in Southern California and we are building upon those teachings. Mechanics down this way still have fond memories of you, and still comment on how great the classes you taught here were. Thank you for your positive comments, which mean a lot coming from you. And we welcome any comments, suggestions or ideas you may have to keep the webpage quality up for bus Technicians. A pleasure to have worked with you and look forward to work with you in the future.

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