Engine coolants (like antifreeze) have one function: they draw heat away from the engine so the engine can operate more efficiently and malfunctions or damage to the engine parts can be avoided. A cooling system uses water pumps, hoses, thermostats and a radiator, but the primary part is the coolant chemical itself, a substance which keeps the engine from boiling in the hot days, freezing in the cold days and corroding or building up scale while running.
Traditional antifreezes and engine coolants use a glycol base that is made from petroleum, with a more green option available using inorganic compounds that worked well, but need to be replaced much more often. Many times, users would have to add in silicate compounds to improve engine protection, which were available in high and low concentrations. As technology improved, engine coolant began to be sold as fully formulated, all ingredients added in beforehand in the proper amounts so the coolant was ready to go. This is where OAT, or Organic Acid Technology, comes in.
OAT coolants are based on completely different chemistry from older coolants. Instead of using mineral-based additives like borate, nitrite or phosphate to protect the metals of the engine, OAT coolants use a combination of carboxylic and fatty acids instead. This removes the need to add silicate compounds–indeed, it removes silicate compounds completely so coolant no longer needs to be tested or bolstered by continuous additives. This allows the coolant to last for about 6 years (or 600,000 miles) before needing to be replaced.
The fatty acids used in OAT are also generally more kind to the engine than the old mineral-based versions. The old corrosive-protectants often dissolved aluminum pieces, eating them away over time because of aluminum’s peculiar composition, but OAT coolants do not, lowering the build up of aluminum deposits and other similar problems. Also, OAT coolants are better for the water pump and do not interfere with the lubrication of the water pump system, whereas the older coolants would wear away lubrication and require even more additives to maintain a proper balance. OAT coolants are also compatible across a wide range of engines, and different brands can work with different engines without trouble.
There are newer versions of these coolants known as hybrid OAT (HOAT) which combine the fatty acids with other chemicals and minerals to help the coolant take effective more quickly, since the main drawback to OAT is that it slows down the reactive time of the coolant.