7 Different Types of Antifreeze – When to Use What

Please note that some of the images in this article were created with the assistance of AI.

The first thing to clear up in any article about antifreeze is what it is and how it relates to coolant. Coolant isn’t antifreeze; it’s a mixture of antifreeze and distilled water that is far more effective than antifreeze alone in maintaining the necessary constant temperature in your car’s engine. The second thing is that, despite what Bart Simpson would have you believe, the only real antifreeze wine scandal involved Austrian winemakers adding diethylene glycol to their wine. Still, sweet diethylene glycol, a widely used solvent, appears to be only somewhat less lethal than ethylene glycol. Neither is suitable for your kids, your pets, or your fancy French wines.   

What Is Antifreeze?

Antifreeze is a chemical additive used in internal combustion engines to maintain an acceptable, even  temperature range. The additive is a colored liquid designed to help regulate engine temperature and prevent corrosion in your engine.  Although there are different types of antifreeze, all of them begin with ethylene glycol, the chemical blend that makes antifreeze so tasty to pets and handy to murder mystery authors. Indeed, thousands of pets and children consume antifreeze every year, resulting in potentially severe consequences, including death.  Antifreeze, often referred to as if it were the same thing as coolant, is actually the main ingredient in coolant. Coolant, which keeps your engine at a relatively constant temperature. Is half antifreeze and half distilled water. However, like the rest of the universe, this article will use the terms interchangeably except where the different matters are.  

Antifreeze Ingredients

A modern coolant will consist primarily of water, antifreeze, and dye. Today, most coolants are organic, but they aren’t as anti-corrosive as inorganic coolants. Manufacturers use additives to address this issue.  Different additives work best in various settings, so there are many of them. Most of them are environmentally hazardous in one way or another.  Check the manufacturer’s safety data sheet for the significant safety hazards of the formula you use. Among the more common additives are:

Borate

A pH buffer that

• • Lowers the freezing point
  • Increases the boiling point
  • Reduces friction
  • Prevents high temp corrosion
  • Eliminates unpleasant smell
  • Prolongs coolant storage life
  • Can damage older engines designed for inorganic coolant

Nitrite

An acid that protects iron from corrosion and the formation of tiny bubbles (cavitation). Common in coolants for older engines and diesel engines. Not typical for newer engines because of their incompatibility with aluminum.

Phosphate 

Fast-acting acid that protects some metals from corrosion is found in IAT coolants. Prone to flaking and scale formation, especially when used with hard water.  

Silicate

Similar to phosphate but damaging to gaskets.  

Sodium Benzoate 

An odorless powder combining benzoic acid and sodium hydroxide found in everything you’ve ever heard of, including soft drinks, packaged foods, cough syrup and pills, oral hygiene products, baby wipes, and, you guessed it, coolants for hybrid engines. Sodium benzoate prolongs coolant life and protects against corrosion, but it becomes destructive when exposed to aluminum and hard water.  

Dyes 

All antifreeze/coolant mixtures are colored with dyes to distinguish formulas from one another and to make it easy to identify a spilled or leaked liquid as coolant.   In other words, it’s crucial to know your additives and pick the coolant with the right ones for your engine. Your owner’s manual will contain the solution to this mystery. 

When Do You Need Antifreeze/Coolant?

Unlike what the name might imply, your motor vehicle needs antifreeze or coolant all year round in whatever climate you live. Antifreeze or coolant helps to protect your engine from corrosion, prevents rust and scale buildup, and helps transfer heat.  In addition to keeping liquids in your engine from freezing in extreme cold, antifreeze also prevents overheating by raising the temperature at which the water in your cooling system will boil. Because it’s important all year, you should check your coolant in the spring and fall to make sure it’s ready for summer and winter.  

Types of Antifreeze

The main differences among the various types of antifreeze are the additives mixed in with the ethylene glycol and water. These are the primary types of antifreeze.

1. Inorganic Additive Technology (IAT) – Green, generally used in older vehicles. 

IAT coolant/antifreeze is the oldest blend and the most common variety. IAT coolants have been used for decades and are proven to provide high levels of corrosion protection. IAT works well with cast iron engine blocks and copper or aluminum radiators.  Most domestic manufacturers stopped using it by the mid-1990s. Asian and European manufacturers stopped in 1990. If not replaced every two years, IARs can degrade cooling systems and cause heater core blockages.

2. Organic Acid Technology (OAT) – Orange, red, blue, or dark green, used in GM, Saab, and VW vehicles

OAT coolants have no phosphates or silicates and are found in most domestic cars made since 1994. The extended coolant life of 5 years or 150,000 miles is an extra benefit of OAT coolants. Dex-Cool is an OAT coolant used in GM cars.  Problems arose when owners added green coolant to Dex-Cool systems, causing blockages. It remains an acceptable coolant but cannot be mixed with any other type of antifreeze.  

3. Hybrid Organic Acid Technology (HOAT) – Yellow, used in Ford, Chrysler, and European vehicles  A phosphate-free blend is Turquoise and used in Asia

Commonly installed in newer Chrystler models, HOATs are between IAT and OAT coolants. IAT was good at anti-corrosion but needed frequent changes. OAT lasts a very long time but isn’t so good at preventing corrosion.  Mixing the two only worsens the corrosion, so that wasn’t the solution. However, the chemical composition of HOAT keeps rust and buildup down, works at low and high temperatures, and lasts at least five years.  On the other hand, HOAT does not work and play well with others. Manufacturers recommend not mixing them. Severe buildup and effectiveness problems can develop, even if you’ve drained the engine first.  If, for some reason, you insist on making the switch, be sure to flush the system before doing so and be aware that you may still have problems.  

4. Phosphated HOAT (P-HOAT) – Pink or Blue, used in Toyota, Nissan, Honda, Hyundai, KIA & other Asian vehicles

Required in most Asian vehicles, P-HOAT uses a mix of phosphates and carboxylates as corrosion inhibitors. Asia generally has softer water than Europe, thus avoiding the problems European vehicles encounter with phosphate coolants.  

5. Silicated HOAT (S-HOAT or Si-HOAT)  – Purple, used in Mercedes-Benz, Audi, VW, Porsche, others

Primarily used in non-US vehicles, S-HOAT is phosphate-free to respond to the prevalence of hard water in Europe. Hard water commonly contains calcium and magnesium, which react with phosphate and forms calcium or magnesium phosphate.  These chemical products can cause scale formations on engine surfaces and result in performance problems. Thus, European regulations call for a HOAT formula that is phosphate-free.  P-HOAT instead contains a mix of silicates and carboxylates. S-HOAT provides antifreeze service for five years of 150,000 miles.

6. Multi-Vehicle Antifreeze/Coolant – Yellow. 

MVAC coolants use special additives that allow various chemical blends to work together. It is essentially a universal coolant solution for pleasure boats, motorcycles, cars, and light commercial vehicles. MVAC generally helps extend the life of higher-mileage vehicles.  

7. Antifreeze Without Ethylene glycol

Made with propylene glycol and often referred to as non-toxic antifreeze, it is used where antifreeze with ethylene glycol would be too risky or inappropriate. These uses include food-processing systems and home water pipes. The chemical itself is often used in processed foods and electronic cigarettes and oxidizes to lactic acid. A potential hazard in mechanical systems is that it is relatively highly corrosive by creating organic acids. Propylene glycol methyl ether is used in many diesel engines. Finally, glycerol was previously used as automotive antifreeze. It is non-toxic, non-corrosive, and can withstand relatively high temperatures. Today, it is mainly used as an antifreeze in sprinkler systems.  

Choosing Your Coolant/Antifreeze

Whether foreign or domestic, late-model cars come with recommendations for the best coolant to use. Instead of trying to decipher the hieroglyphics on the typical coolant container, reading your owner’s manual might be your best option for choosing a coolant. Your car (if it was new) came to you with the right coolant. If you keep using that same coolant or buy your coolant directly from your dealer’s parts counter, you’ll always be sure to have the correct coolant.   You can mix different brands of coolant (Shell versus Valvoline, for example) so long as they are the same type of coolant and include the same chemical mix. Mixing different types of coolants is not the same thing and will cause serious problems.  The chemicals in the coolants can interact with one another and actually make the problems the coolant is supposed to solve worse. These chemical reactions may actually create solid particles that can act like sandpaper in your system, destroying seals and other components.

Antifreeze Colors

IAT is typically green

OAT is orange

HOAT is yellow

HOAT phosphate-free is turquoise

P-HOAT or phosphate is pink or blue

Si-HOAT or silicated is purple

What Make Of Cars Uses IAT Antifreeze?

IAT antifreeze is typically used in older cars. For example, IAT was used by Ford and Chrysler until 2001, except for some 1999 models using OAT or blue coolant specifically made for Ford. GM used IAT antifreeze until 1994.  The reason older cars used IAT is that their engine and components were constructed of cast iron, copper, brass, and aluminum. The silicates in the ethylene glycol protect these highly diverse metals from corrosion. It’s recommended that older cars have their antifreeze changed every 36,000 miles or three years, whichever comes first.

IAT Pros And Cons

The pros are written above, but the cons include the rapid breakdown of the additives. This means the antifreeze should be changed every two years of 24,000 miles before the engine is damaged.

What Make Of Cars Uses OAT Antifreeze?

“Newer” cars are defined as being made from 1995 up to the present. OAT antifreeze was used in GM vehicles from 1995 up to the present. From 1996 up to 2001, it was used in Audi, Mazda, Land Rover, Honda, Kia, Toyota, Porsche, Saab, Volkswagen, and Jaguar. Cars made from 2000 up to the present use OAT due to its superior engine protection.  In GM vehicles, the brand is called Dex-Cool. To other makers, it’s called propylene glycol. The protective additives were made to be slow-acting, which is why it’s recommended that the antifreeze be changed every five years.

OAT Pros And Cons

The advantages of using OAT antifreeze are the superior corrosion protection and the long life of the antifreeze. The disadvantages of using OAT antifreeze are that it’s a bit costly, availability is limited, as well as being incompatible with other types of antifreeze in older engines and cooling structures.

What Make Of Cars Uses HOAT Antifreeze?

HOAT is where the “t” in “technology” really makes a splash. Hybrid electric cars make electricity completely different from other machines. The water added to the antifreeze running through the engine creates electricity. This process puts a severe strain on the rubber hoses and aluminum engine parts from the inside to the outside. It’s called electrochemical degradation or ECD. So, carmakers came up with a coolant that would satisfy “global” car requirements from “G-05” to “G-11” and “G-12.” This addresses the problem for European makes of cars like Audi, Volkswagen, Mercedes, BMW, Volvo, and Saab along with American cars such as Ford and Chrysler. HOAT comes in pink, blue, red, orange, and yellow, but don’t go by the color. Make sure to read the container. Look for the “global” and “G-11” or “G-12” distinctions to be sure it’s right for your car. It’s recommended that the antifreeze be changed every five years or 50,000 miles.

HOAT Pros And Cons

HOAT’s advantages lie in its ability to keep rust and corrosion under control, it operates just as well at low as well as at high temperatures, and it lasts for five years. Its cons, however, are pretty serious. HOAT has the capacity to cripple the cooling system with gunk. Flushing the system doesn’t always help, because remnants of the chemical cling to pathways.

What Make Of Cars Uses P-HOAT Antifreeze?

The heat from the outside does just as much damage to the engine components as heat from beneath the hood. You’ll need extra ingredients in the antifreeze to tame the beast. The addition of phosphates and carboxylates instead of silicates provides excellent corrosion protection. You’ll find P-HOAT used in cars made in Asia, such as KIA, Toyota, Honda, Nissan, and Hyundai. P-HOAT comes in pink or blue.

P-HOAT Pros And Cons

The only con of P-HOAT antifreeze is deficient heat transfer. That’s the reason silicates aren’t used in Asian antifreeze.

What Make Of Cars Use Silicate HOAT Antifreeze?

The difference between silicates and phosphates is that phosphate is organic and silicate isn’t. They both protect a car’s engine, though, depending on the metals involved. The newest in antifreeze technology, it’s a deep purple and used in Mercedes, Audi, VW, Bentley, Lamborghini, and Porsche. It’s recommended that the antifreeze be changed every five years or 150,000 miles.

Si-HOAT Pros And Cons

While silicates do protect an engine from corrosion, they tend to form a sand-like substance at the end of their useful life. Silicate, after all, is abrasive and tends to damage seals. It gunks up everything from the water pump to the rest of the cooling system. It’s a good idea to strictly adhere to the changing schedule to avoid this kind of thing.

The Difference Between Antifreeze And Coolant And Why It Matters

Numerous drivers use the terms coolant and antifreeze interchangeably, but the truth is they’re different. Antifreeze is a concoction of ethylene glycol or propylene glycol. Coolant is created when water is added to the antifreeze. Here’s why. Water boils at 212 degrees and freezes at 32. Antifreeze alone boils at 129 degrees and freezes at 0 degrees. Water alone causes rust and corrosion to an engine. Antifreeze alone won’t cool the engine, since engines run at around 200 or more degrees. Antifreeze and water must be mixed 50-50 in order to stabilize the boiling point and freezing point for the engine’s and cooling system’s optimal operation. This is why it matters.     • Freezing point. If you drive a car in below-freezing conditions, then you need to mix water with antifreeze to lower the freezing point. The proportions of the mix are vital to the survival of the engine. An improper mix damages the engine.     • Heat transfer. The opposite side of the coin is heat. Driving in summer with the A/C blasting, the bass in the music pounding, and the GPS/Phone Calls/Rearview Cameras going all draw power from the engine. Antifreeze alone can’t transfer the heat generated away from the engine in any kind of proportion, so mixing it with water accomplishes this transfer way better.     • Engine protection. The additives in the antifreeze are there to prevent engine corrosion. If the antifreeze isn’t mixed with water, the additives settle to the bottom of the antifreeze chamber. Mixed with water, the additives won’t settle and will protect the engine from rust and corrosion. Tip: Shake the antifreeze container before adding water and antifreeze to the car. This mixes any additives that might have settled at the bottom of the container. 

Have You Heard Of Waterless Coolant?

Which brings us to a product on the market that blows the above information out of the water, if you’ll pardon a terrible pun. How can a car’s engine not overheat with no water in the mix? It won’t overheat when the product is made of 100 percent ethylene glycol or polyethylene glycol. There would be no corrosion at all, the heat transfer would be more stable, there would be no pressure if you wanted to open the radiator to top off your antifreeze, all added to the fact that waterless coolant boils at 375 degrees and freezes at 40 below. Water can’t say that. So, what kind of vehicle would use this waterless coolant? Racing vehicles, ATVs, UTVs, classic cars, snowmobiles, and other sporting vehicles require such temperature and pressure considerations, so waterless coolants are the ideal solution. While all these points have good “pros,” the cons should receive equal attention:     • Price. Waterless coolants https://greengarageblog.org/17-waterless-coolant-pros-and-cons are double the price of ordinary coolants. For diesel engines or big rigs, make that ten (I’m not exaggerating) times the price.     • Availability. Ordinary antifreeze is available even in grocery stores, but waterless coolant isn’t. If you don’t stock up when you make the conversion from antifreeze to waterless, then possibly expensive repairs will be involved. Better safe than sorry.     • The vehicle’s fan. Since the heat profile will be different with waterless coolant, the vehicle’s fan could be triggered and run continuously. Let a professional set the timing and temperature profiles of the vehicle to avoid these kinds of things.

A Short History Of Antifreeze

Charles-Adolphe Wurtz, a French chemist, first made ethylene glycol in 1856 in Napoleonic-era Paris. Nothing much happened with it until the late 1800s into the early 20th century, when early cars used various solvents to prevent engines from overheating. They corroded rather badly, though. Fast forward to WWI, when ethylene glycol was used in the manufacture of explosives. The chemical is used heavily in WWII. It began to be used in cars around 1926 as an antifreeze to keep the engine viable. Now it’s late in the 20th century. Ethylene glycol and its cousin polyethylene glycol are used in the formulation of plastics, polyester textiles, some types of inks in stamp pads, film, paint, ballpoint pens, cosmetics, solvents, and it’s also used in the pharmaceutical industry. It’s used in antifreeze and made into various types. Note: Pet owners and parents, take serious note. Antifreeze is deadly to children and pets. Animals are drawn to the sweet taste of the chemical. It kills within minutes. Children are curious about every little thing, so the first thing they’ll do is dip a finger in it and taste it.  Get on the Poison Hotline at (800) 222-1222 and follow their directions minutely, and your pets or children could be saved. If you notice a leak or spill, get it up immediately and dispose of it in a responsible manner.

Antifreeze FAQs

I Know Antifreeze Is Toxic. Is It Flammable?

Yes. It sounds odd to say that something with water in it is flammable, but the truth is that glycol is flammable. Relax, it has to reach 650 to 750 degrees before it catches fire, and your car only gets up to around 250 degrees. Caution is always the best thing, though, so don’t take any chances.

How Will I Know Which Antifreeze To Use In My Vehicle?

Carmakers know of what metals their engine components are made. They know which antifreeze additives will best protect them and for how long. Ask at the dealership or follow the advice in the car’s owner’s manual for the best results.

How Does A Cooling System Work Anyway?

The cooling system includes the radiator, various hoses leading to the water pump, fans, the thermostat, and the antifreeze. The cooling system takes away the excess heat generated by the engine and maintains just the right temperature, gets the engine to the right temperature when the car is started and keeps it warm in winter.

Is There A Difference Between Ethylene Glycol And Propylene Glycol?

Ethylene glycol has a little higher boiling point than the other and is more expensive to make, although it’s widely used. Propylene glycol is somewhat less toxic.

Can You Mix Ethylene Glycol-Based Antifreeze With Propylene Glycol-Based?

The two are chemically close, so they can be mixed without harm to the cooling structure. While ethylene glycol has greater heat transfer capability, adding propylene glycol to ethylene glycol doesn’t cancel out ethylene glycol’s toxicity.