By Jim Marotta

Back in the day, no matter which brand you chose, antifreeze was green. The glycol-based formula contained silicates as corrosion inhibitors. You mixed the antifreeze 50/50 with water and poured it in the radiator. As the engine operated, the antifreeze performed its primary duties of carrying heat to the radiator, preventing freezing (hence the name) and protecting against corrosion in the cooling system. You simply changed the antifreeze at the prescribed service interval.
Today, with different types of antifreeze technology in a rainbow of colors, confusion abounds among automotive people and consumers alike as to what color antifreeze is best. The easy part is that most antifreeze manufacturers still make coolant with ethylene glycol (EG), a type of alcohol made from ethane. Manufacturers also make more environmentally friendly versions with less-toxic propylene glycol (PG), a similar compound made from propane.
Evolving Antifreeze
Inorganic Acid Technology (IAT) is the chemical basis for the traditional green antifreeze. IAT contains either EG or PG and is usually fortified with silicate or phosphate additives to make it compatible with metal cooling system components. The generally recommended replacement interval is every three years or 36,000 miles. The owner's manual or maintenance chart from and shows what the vehicle manufacturer recommends for each specific vehicle.
Inorganic acid technology is the chemical composition for the traditional green or yellow antifreeze (right). Organic acid technology is the orange coolant on the left.
Organic Acid Technology (OAT) is a Long Life Coolant (LLC) / Extended Life Coolant (ELC) widely used in Europe before its introduction in North America. OAT is usually EG. The generally recommended replacement interval is five years or 150,000 miles; find out what the vehicle manufacturer's recommendations are for your car or truck.

An example of an organic acid technology long life/extended life coolant.
Hybrid Organic Acid Technology (HOAT) combines IAT and OAT with nitrites. Antifreeze manufacturers often refer to it as "global," indicating on the bottle that it meets or exceeds the specification "G-05" for most vehicles newer than 2002 and "G-11" or "G-12" for Volkswagen and Audi. The generally recommended replacement interval is five years or 150,000 miles, always check your vehicle manufacturer's recommendations for your car or truck.
Why All the Different Coolant Formulations?
In the early 1980's Ford was working with antifreeze manufacturers to come up with a formulation to meet global needs. European countries had very hard water and since water is 50% of the antifreeze mix, water quality dramatically affects the overall mix. As European manufacturers were abandoning phosphate-based technology because phosphates tend to form scale, Japanese manufacturers were moving away from silicates, which tend to destroy water pump seals.
The first alternate coolants were hybrids combining carboxyl and silicate technologies. Ford started using them after extensive durability testing (more than 40 million fleet test miles on every vehicle platform that Ford had) in the early 1980s. At about the same time, Mercedes and VW were also using hybrid formulations.
In addition to better corrosion inhibitors for the global market, other issues precipitated formula change. Toxicity and environmental concerns are behind the use of PG rather than EG, while the promise of longer-lasting engine protection and less maintenance spur development of the newest formulations, such as Nissan's new blue coolant, which is designed to last ten years or 135,000 miles.
Does Antifreeze Break Down?
Engine antifreeze does break down, forming corrosive organic degradation products. Antifreeze buffering agents inhibit this corrosion. Since most antifreeze leaks out of the vehicle (according to the EPA, only 12% of antifreeze produced in the U.S. is recycled), most systems are "topped off" with fresh antifreeze, extending its life somewhat. How much depends on the type of antifreeze added.
Can You Mix Antifreeze Technologies?
The one universal coolant that all agree on is water. For best performance, water needs a little help. What happens when antifreezes are mixed? A lot of the confusion about mixing coolants stems from early work with carboxyl coolants. In an American Society of Testing and Materials (ASTM) test, mixing IAT and OAT coolants resulted in more corrosion than either antifreeze alone. Subsequent tests revealed a testing error: the corrosive environment occurred because the coolant was too dilute.
It is best to use the same type of coolant originally used in your car or truck, or the vehicle manufacturer's current recommendations. According to industry experts, if you do not know what coolant is in the vehicle and you top off with another brand, nothing bad is going to happen. Only when dilution rates border 50% is the effectiveness of each coolant's inhibitor package compromised. However, when mixing coolants, the recommended coolant change interval will degrade to that of the shorter-life coolant.

Proper Maintenance is Key

As with anything automotive, proper maintenance is the key to longevity. More important than the type of antifreeze you use is to maintain the cooling system properly by maintaining freeze point protection and proper coolant level. Almost all coolants work best at the ideal freeze point mixture, which for most parts of the country means a 50/50 antifreeze-to-water mixture. At this level, antifreeze protects to -34 °F and boil-over protection to 257 °F. In addition, maintaining proper freeze point protection ensures corrosion inhibitors are present at intended levels.
Maintaining the cooling system properly by maintaining freeze point protection and proper coolant level is critical. Here a handy tool provides coolant concentrations.
Vehicle manufacturers design cooling systems to operate full of antifreeze. A system that is constantly low on coolant can create an extremely corrosive environment due to the aggressive nature of the vapors of a glycol/water mix. These steam vapors are more corrosive than either fluid by itself. To check your coolant system capacity, simply refer to your vehicle's cooling specifications at,, or your owner's manual.
If you choose to maintain your cooling system yourself, keep in mind that all types of antifreeze are poisonous. Animals and humans can be attracted by its sweet taste. Used coolant is extremely toxic and an environmental hazard, always recycle it properly.

Tap Water Won't Do

In almost every part of the country, tap water contains minerals such as magnesium and calcium that can form deposits in a cooling system, especially on the engine's hottest parts. The water you use to mix the antifreeze is critical. Premixed coolants are mixed at the factory with distilled water. Use distilled water, not tap or filtered water, when you refill any cooling system.
A system that is constantly low on coolant can create an extremely corrosive engine environment.
Coolant Keeps Working After the Engine Quits
Having the proper coolant level is still important after shutting off the engine. As the coolant stops flowing and the engine temperature increases dramatically, areas of localized boiling can send large shock waves through the engine wreaking havoc on components, especially those made of aluminum.
A subscription to ChiltonDIY or ChiltonPRO, with comprehensive maintenance charts and fluid capacity specifications, will give you all the information you need to keep your cooling system in top shape.

A muscle car enthusiast and drag racer, Jim Marotta is a freelance automotive writer with more than 20 years experience in the automotive industry.