Some misinformation about dex-cool here.
So GM decided to make a solution of additives to ethylene glycol which would allow less time between coolant changes. Oldskool ethylene glycol contains phosphates and silicates, which after binding to heavier metals like Iron or other hard metals in water, slightly precipitate out of solution, meaning we need to change our old coolants more often.
What is GM 'dex-cool'. It's a mixture of additives in ethylene glycol. What's the big deal about the additive? It's a hydrocarbon chain acetate (acid) which has a coordinating alkaline metal, sodium or potassium 2-ethylhexanoate. The original idea was to create a mixture of additives which would sequester metal ions from hard water. The intent was to decrease the amount of rust (Iron III Oxide) while increasing solubility of the metal-organic compound in solution. This would equate to a longer service life, and I'm pretty sure GM was the pioneer in this area.
So they found a new mixture of acids/acetates which are more soluble with their large alkyl/greasy group chains in a solution of ethylene glycol. And it backfired. Oldskool gaskets are made from, among other synthetic rubbers, nylon which contains an amide and the polymer is easily broken (hydrolyzed) by acids in solvents which can hydrogen bond (hydroxylic solvents, here it's the glycol). Add to this that rate of hydrolysis increases with temperature, and bad things happen, meaning gaskets are chewed up and dissolved, coolant leaked into the oil, loss of coolant in passages allowed for rust pockets to build up and clog passages, and blown head gaskets for all.
What they did to fix it? They took out a few original additives, sebacic acid and tolytriazole, which have the not-so-convenient effect of polymerizing or forming adducts with hexanoic acid (2-ethylhexanoate), and so the additives are used up rendering them useless, also gaskets are now made from entirely different polymers and the giant fiasco has been quenched.
However, if you do run acidic dex-cool in a motor with oldskool (or cheaper) glycol and additives, then huge globs of nasty precipitate will form with acid and silicates or phosphates.
Now, GM is pretty solid on the formulation after checking a bunch of different countries ACDelco MSDS's and aftermarket MSDS's for dex-cool, they're all similar. It looks like ACDelco brand has replaced some hexanoic acid with neodecanoic acid (a sodium acetate) and this may increase solubility of the first acid in glycol. I did notice prestone dex-cool contains a nitrite additive, and don't know if this is the best dex-cool of choice with aftermarket nitrile gaskets, or in fact why they're using it.
I'm not going to go into the chirality of the additive and how entantiomeric mixtures widen its effective solubility range. For now, it works, and ACDelco IMO looks the best.
Problem with our cars? If we lose coolant somewhere, maybe faulty water pump gaskets, who knows, then we introduce air/steam pockets where rust builds up and clogs coolant passages, kind of like thrombosis or arterial embolism in our own arteries. Solution? keep it topped off with ACDelco Dex-cool until GM finds the solution to our slow leak. Don't open the cap often to prevent water from condensing inside the system and when you do wait for it to cool, basically everything we already know.
I is a chemist.
