[Buford T. Justice]

Most universal automotive coolants using organic acid technology contain...

Ethylene Glycol (107-21-1)
Diethylene Glycol (111-46-6)
Sodium 2-Ethyl Hexanoate (19766-89-3)
Sodium Neodecanoate (31548-27-3)

I have seen some use Potassium 2-Eythl Hexanoate (3164-85-0).

In this regard, what is the difference between sodium and potassium?  I know potassium has a more violent reaction in water than sodium, but in coolant these are used as salts.

[Arkcon]

Correct, the salt properties, or the ion properties don't take on the element's properties.  Usually we use the sodium salt, it is simply cheaper, eventually traced back to feedstock chemicals, that trace back to NaCl -- we have oceans full of that.  Potassium salts are often more pricy -- we use those for fertilizer to grow food.  Sometimes we use one salt over the other for solubility reasons, or because sodium salts are slightly more hygroscopic than potassium -- that's a serious issue for black powder.  But sometimes, its just a coincidence.  Since they're both salts of long organic acids, maybe they have slightly different pKa's and function as a buffer.

[Buford T. Justice]

Thanks for the reply.  A chemist I am not.  Can you also please explain what 2-Ethyl Hexanoate is and does?

[Arkcon]

I can only guess, its a buffer.  As heat damages other molecules, they may form acid or base, which will attack radiator components.  The buffer reacts instead with either acid or base, preventing buildup.  It may also be a scale-remover, a weak acid meant to dissolve corroded parts to avoid blockage.  Or because they are long organic molecules with charged heads, they are detergents which make sure the coolant can penetrate small cavities.