Editing Coolant (section)

==Corrosion inhibitors==
There are many different chemicals used as corrosion inhibitors in engine coolants.  These make up less than 10% of the coolant, with over 90% being the antifreeze.  There are two main classes of corrosion inhibitor, IAT and OAT, but with a bewildering array of combinations, proprietary formulations, names, and colours.

*'''IAT''', Inorganic Acid Technology.  Not actually acids, these are salts of inorganic acids, usually quite alkaline, such as amines, nitrites, phosphates, and silicates.  These are the traditional corrosion inhibitors, effective for all metals, and have an engine service life of up to 2 years or 30,000 miles.  Some downsides are sludging and rusting from as they quickly lose effectiveness, and water pump damage from silicate precipitation.
*'''HOAT''', Hybrid Organic Acid Technology, often called '''Lobrid''' to indicate it being an older technology than hybrids such as P-OAT and Si-OAT.  A confusing term originally used for coolants with inorganic inhibitors that also contained some organic inhibitors, often sodium benzoate rather than a carboxylate, designed to extend the short service life of pure IAT coolants.  The term is now sometimes applied to modern coolants such as the silicated OAT group, but these are a very different set of inhibitors.
*'''OAT''', Organic Acid Technology.  Again, not acids, but salts of organic acids, such as carboxylates, sebacates, and 2-EHA.  These give good protection to ferrous metals and aluminium alloys, but poor for "yellow" metals which use solders.  They have a longer service life, typically quoted at 5 years or 100,000 miles.  These are not safe for use in older engines which contains brass or copper.  Early versions in the US were dogged by reports of corrosion and engine damage, and one of the inhibitors (2-EHA) has been implicated in damage to silicone-based seals and gaskets.  Many modern formulations do not use 2-EHA or have very low levels.
*'''Si-OAT''', Silicate Organic Acid Technology.  "Universal" coolants, safe to be mixed with any other coolant.  These are now added to many new European cars.
* Other types, such as '''P-OAT''' and '''PSi-OAT'''.  P-OAT coolants are found in many Japanese brands, designed for very long service life but somewhat sensitive to use conditions such as hard water.  PSi-OAT is relatively new, but becoming common in European engines.

===Mixing===
It is generally recommended not to mix different coolants even if they are the same colour, although more modern types are increasingly becoming safe to mix with anything.

The "classic" IAT coolants (eg. G11) should never be mixed with the first-generation "plain" OAT coolants (eg. G12).  OAT coolants were then improved (ie. G12+, G30, etc) so that they could be safely mixed with older IAT coolants and the original OAT coolants, albeit potentially with some loss of protection length.  These were further developed to Si-OAT and PSi-OAT coolants, which are also generally safe to mix with most older coolants.  Mixing coolants of radically different colours may produce an unpleasant-looking brown result.

HOAT, PHOAT, etc., may not be compatible with other types, and there are many coolants that don't fit cleanly into any of these categories.  Again the safest advice is never to mix different types.

Although VW G13 and other coolants containing glycerol contain a different combination of antifreezes, it is usually safe to mix them with any other type.