Here's more information than you want about OAT, IAT and HOAT. Context Marin, it's all about context.
Antifreeze is used in cooling systems to both lower the freeze point of water and
raise its boiling point. It is also used as a carrier for different types of additives
such as sodium silicate to protect aluminum from corrosion, anti-foaming agents
and other corrosion inhibitors. Although straight antifreeze actually freezes and
boils quicker than tap water, when mixed with water in the proper proportions (a
50% / 50% mix is ideal) in a cooling system, it greatly increases the cooling
system's ability to perform its designed function of removing heat from critical
engine parts and to enhance the service life of the various cooling system
Inorganic Acid Technology (IAT) is the chemical composition for the traditional
antifreezes that are green in color. An IAT can be used with either ethylene glycol
(EG) or propylene glycol (PG). The normal IAT service life is two years or 30,000
miles (50,000 km).
Organic Acid Technology (OAT) was the first LLC / ELC introduced in North
America in 1994. OAT antifreeze had been widely used in Europe before its
introduction in North America. OAT can be either EG or PG but is mostly EG
based. Its first dye colors were orange and red. These dye colors are still used by
General Motors and Caterpillar. Green, pink and blue have been added to the list
of available OAT antifreezes. It is recommended that OAT not be mixed with any
other antifreeze technology. The normal OAT antifreeze service life is 5 years or
150,000 miles (250,000 km).
Hybrid Organic Acid Technology (HOAT) is a combination of IAT and OAT with
nitrites added. This makes HOAT suitable for use in both light duty and heavy
duty systems. Currently, two manufacturers are using HOAT for their vehicles.
Daimler/Chrysler's version is dyed orange and contains 10% recycled antifreeze.
Ford Motor Companys version is dyed yellow and does not contain any recycled
antifreeze. Both of these HOAT antifreezes use the marketing designator of GO-
5. They are compatible with each other but mixing them with IAT or OAT is not
recommended. The normal HOAT antifreeze service life is 5 years or 150,000
miles (250,000 km).
Nitrated Organic Acid Technology (NOAT) is an OAT with nitrates added. This
makes NOAT also suitable for use in both light duty and heavy duty systems.
NOAT and HOAT are very similar in performance characteristics. Currently, no
OEM vehicle manufacturer is using NOAT. The normal NOAT service life is 5
years or 150,000 miles (250,000 km).