Traditional "Green" Antifreeze
Traditional North American GREEN antifreeze, the original universal formula that everybody used until the introduction of today is extended-life coolants. The fast-acting silicate and phosphate corrosion inhibitors provide quick protection for bare iron and aluminum surfaces, and have a proven track record of providing trouble-free service in virtually any vehicle application (domestic, Asian or European), assuming the chemistry is correct. For example, OAT coolants should not be used in a vehicle that specifies the use of a hybrid OAT coolant. Again, always defer to the owners manual. But the short-lived nature of the corrosion inhibitors means this type of coolant should be changed every two to three years or 30,000 miles (though some products now claim a service interval of up to 50,000 miles with improved chemistry).
OAT-Based Extended Life Coolants
OAT stands for Organic Acid Technology, and includes such ingredients as sebacate, 2-ethylhexanoic acid (2-EHA) and other organic acids, but no silicates or phosphates (except in the case of Toyota's pink extended-life coolant, which adds a dose of phosphate to its extended-life OAT-based antifreeze). OAT-based coolants are usually (but not always) dyed a different color to distinguish them from traditional North American green antifreeze. GM OAT-based Dex-Cool is orange. Volkswagen/Audi uses a similar product that is dyed pink. But Honda has an extended-life OAT coolant that is dyed dark green and does not contain 2-EHA.
The corrosion inhibitors in OAT coolants are slower acting but much longer-lived than those in traditional North American green coolants. Consequently, OAT coolants typically have a recommended service life of five years or 150,000 miles (which ever comes first - which means you should change the coolant after five years and NOT wait until the odometer says 100,000 to 150,000 miles).
OAT corrosion inhibitors provide excellent long-term protection for aluminum and cast iron, but may not be the best choice for older cooling systems that have copper/brass radiators and heater cores. It depends on the formula.
Hybrid OAT or HOAT Coolants
Hybrid OAT coolants, also known as HOAT antifreeze or G-05 antifreeze. This formulation also uses organic acids, but not 2-EHA (different organic acids are used). Hybrid OAT coolants add a small dose of silicates to provide quick-acting protection for aluminum surfaces. Hybrid OAT coolants are currently used by many European vehicle manufacturers as well as Ford and Chrysler.
As HOAT antifreeze ages, however, some of the silicates may drop out of solution. These particles can have an abrasive effect as they circulate in the cooling system, accelerating wear on water pump seals and plastic impellers, plastic radiator end tanks, or inside metal heater cores with sharply curved tubes. To avoid these kinds of problems, most HOAT-based antifreezes use stabilizers to keep the silicates in solution, and they contain only a small amount of silicates. HOAT-based antifreezes that claim to be "low silicate" formulas should meet the ASTM D6210 standard (which is a requirement for most late model diesel engines).
Like-OAT-based antifreezes, HOAT-based antifreezes also have a claimed service life of 5 years or 100,000 to 150,000 miles -- which ever comes first.