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Interesting info found on the net that may remove confusion about which type of coolant is the proper coolant to use.

The main ingredient in the vast majority of automotive antifreeze on the market today is ethylene glycol. Virgin ethylene glycol is produced from ethylene which is produced in the petrochemical industry by steam cracking. Steam cracking is a process that reduces complex hydrocarbons into simpler hydrocarbons, and is used to produce the many products that come from crude oil and other complex hydrocarbons. (Jet fuel, gasoline, diesel fuel, motor oil, ethylene and propylene glycol, etc.)

The main uses for ethylene glycol are listed below.


The major use of ethylene glycol is as an automotive antifreeze. Due to its low freezing point, it is also used as a deicing fluid for windshields and aircraft. Ethylene glycol is also commonly used in chilled water air conditioning systems that place either the chiller or air handlers outside, or systems that must cool below the freezing temperature of water.


Ethylene glycol has become increasingly important in the plastics industry for the manufacture of polyester fibers and resins, including polyethylene terephthalate, which is used to make plastic bottles for soft drinks. The rapidly expanding economies of China and India have led a worldwide increase in demand for ethylene glycol, and have helped to fuel recent price increases.
The antifreeze capabilities of ethylene glycol allow it to be used for airplane deicing and have made it an important component of vitrification mixtures for low-temperature preservation of biological tissues and organs.
Obviously, the purity requirements for soft drink bottles, deicing and preservation of biological tissues is much greater that it needs to be for automotive antifreeze or chiller fluid, and virgin EG is required for those applications.

Antifreeze Types

Automotive antifreeze/coolant is made of ethylene glycol, water, and a chemical additive package. For many years, there was only one type of antifreeze on the market, conventional green. Antifreeze technology, however, has become significantly more complex in the last several years with the introduction of Dexcool and other extended life antifreeze formulas. There are three main types of antifreeze on the market. They all contain an ethylene glycol base, water, dye and an additive package. Colored dye is added for leak detection and is not a reliable way of identifying coolant type. The additive package is what makes them different.

Conventional green antifreeze formulations usually contain a number of inorganic corrosion inhibitors that provide immediate corrosion protection because they maintain the pH of the solution (buffer it), but are consumed or transformed chemically as they perform their functions. As the coolant is heated and cooled, and exposed to air, the components of the conventional antifreeze additive package are depleted over time. This causes the pH to drop, and is why the coolant should be changed out every two years or 24,000 miles.
Dexcool-type extended life coolants use organic acid technology to inhibit corrosion, and are referred to as OAT based coolants. OAT antifreezes are touted as having longer potential service life than conventional antifreezes because of the fact that the components in the additive package are not chemically consumed as they perform their function of inhibiting corrosion. The chemicals used in the OAT type formulas protect metals from corrosion by forming a thin, molecular coating on them, and because of this, are not as fast acting as conventional inorganic formulas. However, as long as the cooling system is kept sufficiently full and coolant is not lost due to leakage nor diluted by top-off with water or conventional antifreeze, it will continue to function properly. Unfortunately, if the cooling system is not properly maintained, a “red muck” is likely to form and could cause serious cooling system problems.
The third type of antifreeze on the market today is the hybrid OAT, known as HOAT (or G O-5). One of the primary problems with OAT formulations is that they are not compatible with conventional antifreezes. The chemicals used in OAT antifreeze react to some extent with some of the inorganic salts and other components in conventional antifreeze. The result of this interaction is the generation of cloudiness and precipitates. HOAT formulations are called hybrid because the additive package contains ingredients from both OAT and conventional formulas and is compatible with both.
Hybrid OAT antifreezes provide both fast acting and extended life corrosion protection, eliminate the problem of anti- freeze compatibility, and therefore are compatible with all types and colors of antifreeze.
Unfortunately, many automotive professionals consider all extended life antifreeze to be “Dexcool” and associate all the problems related to “Dexcool” with both OAT and HOAT formulas. The result of this misconception is often replacing the extended life coolant with conventional green. Industry experts say that this can be done safely if all of the green antifreeze is removed from the system. However, auto manufacturers recommend specific formulations and replacing the factory fill coolant with a different type that doesn’t meet the manufacturer’s specifications could cause liability issues down the road. A much safer solution is to replace OAT systems with HOAT coolant which meets OAT specifications.

In the Cooling System
Regardless of the type of antifreeze used, the additive package will eventually break down and cease to provide adequate corrosion protection. The antifreeze will also pick up contaminants from the engine cooling system. In other words, antifreeze wears out and gets dirty. The service life for conventional green antifreeze is 2 years or 24,000 miles, and for OAT and HOAT is 5 years or 150,000 miles, and the manufacturers recommend fluid replacement at these intervals. However, although the antifreeze loses its corrosion protection and picks up contaminants, the ethylene glycol base does not break down and remains intact. In other words, the ethylene glycol retains its ability to lower the freeze point and raise the boiling point of the solution. This simple fact is the basis for the antifreeze recycling industry.
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