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Antifreeze, Colors Like a Rainbow - The mystery of the varieties of engine coolant

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  • Antifreeze, Colors Like a Rainbow - The mystery of the varieties of engine coolant

    This was copied from and originally posted at

    By Jim O'Clair from December 2006 issue of Hemmings Motor News

    Although ethylene glycol has been around since the 1850s, it was not considered for use as an automotive coolant until World War I when it was used in military vehicles to prevent radiators from icing up overnight. Initially, it was used as a substitute for glycerol, a component in explosives. American production cars did not begin using any antifreeze until 1923, when an ethylene oxide-based coolant was first used. Ethylene glycol, the green antifreeze we have all been using for as long as we can remember, did not replace ethylene oxide as the industry standard until 1937. Life was simple then, just mix one part of the green stuff to one part water, and you were good to go for up to three years. Occasionally, you would check the potency of your mixture with a bulb-type antifreeze tester and maybe add a little to give you a little more protection, but that was about it.

    In recent years, there have been many changes, given the new developments in the area of engine coolant. Several manufacturers are specifying their own type of antifreeze, and it can be confusing to the consumer as to which color or formulation of coolant is acceptable for their car. Some European coolants are based on a different pH scale from those made for American cars, because of the differences in plain water between the two continents. This adds to the consumer's confusion.

    All antifreeze falls under one of three basic types. We will give you a brief understanding of each and why they are not compatible with each other.

    Inorganic Acid Technology (IAT)

    This is the common green stuff original equipment manufacturers have used for over 70 years. Ethylene glycol is its base chemical, and there are silicate and phosphate additives that make it compatible with copper, brass, cast-iron and aluminum cooling system components. Manufacturers recommended that you change the green IAT antifreeze every 36,000 miles or three years. IAT coolant was used in GM vehicles until 1994. Chrysler used green IAT fluid until 2001, as did Ford (with the exception of some 1999 models that used OAT blue coolant which must be purchased from Ford).

    Organic Acid Technology (OAT)

    Commonly referred in GM vehicles by the brand name, Dex-Cool or to other manufacturers as propylene glycol. GM introduced Dex-Cool in 1995 as an "extended life" coolant, though most GM car owners and repair shops are finding that Dex-Cool is good for only about three to five years before it needs to be replaced. But because of the additives in the Dex-Cool orange antifreeze, you do not want to substitute the old reliable green coolant. Usually (but not always) dyed orange or yellow so you could tell the difference between OAT and IAT, this coolant has similar corrosion protection to the green stuff; however, it is designed to be slower acting, hence the extended-life moniker. It is made from a propylene glycol base, which makes it less poisonous than conventional IAT for children and pets. OAT, when spilled or lost due to a boil-over, is much less harmful to the environment. In addition to its use in 1996 model year and newer GM cars and trucks, OAT is also used in 1996 to 2001 Audi, Land Rover, Nissan, Mazda, Toyota, Honda, Kia, VW, Jaguar, Saab and Porsche. Manufacturers are now recommending your OAT coolant be changed every five years. OAT coolants are currently readily available from most auto parts stores.

    Hybrid Organic Acid Technology (HOAT)

    This coolant is usually dyed yellow but comes in other colors like green, pink, blue, red and orange, which leads to a lot of confusion. One way to know for sure if you are getting HOAT will be by the packaging. Manufacturers often refer to this antifreeze as "global" and will indicate on the bottle that it meets or exceeds the specification "G-05" for most European cars and G-11 or G-12 for Volkswagen and Audi. Hybrid antifreeze has added silicates for aluminum protection and is advertised as having a five-year change interval. Normally, HOAT coolants are specified for vehicles newer than 2002, specifically Mercedes, Volvo, Ford, VW, Audi, Chrysler, BMW and Saab.

    The use of OAT and HOAT coolants can extend the life of rubber coolant hoses, because they conduct less electrochemical degradation or ECD than the conventional green antifreeze. ECD is the process by which the motion of coolant and water through your engine creates an electrical charge similar to a galvanic battery. This electrical charge degrades both rubber and metal parts in the cooling system from the inside out. ECD can be attributed as the cause of many premature coolant system failures. Volkswagen, Audi and other European vehicles use antifreeze that can be blue, pink or red in color. Most of these are available under the brand name Pentosin in 1.5-liter bottles. The pink and red are specifically designed for alloy engines and both meet the required G-12 coolant specification. The blue is also for alloy-based engines, but with a different pH level, and is equivalent to the G-11 rating.

    You will find other types of antifreeze available for heavy-duty trucks. Both pink antifreeze (no, not the same stuff as used in the toilet in your camper at the lake house) and red are sold for truck use. These should not be confused with the pink or red HOAT coolants used on imported vehicles because they are designed specifically for trucks. These coolants will usually say "low-silicate" and "final charge" or "fleet charge" on them. They will do you no good in your passenger car because the lubrication and metal protection additives are separate in large truck cooling systems.
    So what should you use? Manufacturers will tell you to stick with what is in there. You can have the cooling system cleaned with a coolant filtration system. This is a very popular tool in repair shops today and will recycle your antifreeze. Component chemicals can be re-added to boost its boiling and freezing point and adjust the pH of the cooling system back to specifications. The most accurate tool for measuring OAT and HOAT potency is a refractometer, which is an expensive piece of equipment, so you should have the coolant checked by a service station before deciding whether it should be replaced or refurbished. If you are low on fluid or have a leak, a general rule of thumb is, green IAT is always replaced by green IAT coolant. Dex-Cool or an OAT product with equivalent specifications is always necessary to replace orange or yellow organic-based antifreeze. For the rainbow of colors of HOAT, your only substitute is the yellow or amber global antifreeze. Global coolant will not change the color of the stuff that is already in there. If original red, blue or pink antifreeze is desired, you must get these from a Pentosin supplier or your car dealer. Can you run organic coolant in an earlier vehicle? Yes and no. OAT will work if your radiator is aluminum and you flush your entire cooling system with water and completely refill with OAT, but there are some issues with the interaction between organic coolants and lead solder, so using OAT in a copper radiator is not recommended. In short, antifreeze these days is a buyer beware deal. Check your owner's manual for the correct fluid, and read the label on your replacement coolant carefully to ensure it meets with the required specifications.