After this inconclusive goofing around, more research is clearly needed.
What the heck is "non-silicate, non-borate, non-amine, hybrid organic acid
technology" anyway?? Why is there so much mythology and disinformation
floating around about coolants? Well, the fact is that coolant chemistries
*and* engine/radiator metallurgy have changed rather radically in the last
decade, and the fact that a fill of coolant now has an expected 100,000 mile
or more corrosion-resisting service life is somewhat amazing in its own right.
It's definitely cut into the classic radiator flush-n-fill service upsell
that so many garage guys are used to suggesting to customers, so there are
significant forces at work to keep the coolant-change mystique alive as long
as possible, but it seems that at this stage of the game it's about as
present-day as carburetors and mechanical spark advance.
There are a few fundamental but often subtle facts that come into play, and
there's much more to be found under "coolants" in the
Water is an excellent thermal transfer medium, but has a limited useful
temperature range. Ethylene glycol is about the best anti-freeze and
anti-boil agent to help widen the usable liquid-phase temp range, and when
mixed with between 40 - 60 % water provides excellent thermal protection and
retains the good heat-carrying characteristics of the water. [The less toxic
propylene glycol runs a close second in freeze/boil protection, but is more
expensive and thus far less commonly used.] However, such a mix alone
provides little protection against corrosion, so a package of supplemental
coolant additives [SCA] needs to be added as well to be suitable for use in
systems with metal piping and passages.
The water used really should be distilled or deionized, as it is much less
reactive to metals than tap water which contains random dissolved minerals
and ions. This is one reason Toyota's SLLC comes pre-mixed, to be more sure
that the right type of water is already in there and doesn't fall prey to
just any old thing being added in by a third party.
Metal corrosion inside radiators and engines is greatly accelerated by an
acidic environment, which tends to pull even more ions into solution. Thus,
coolant formulations tend to run fairly basic, and have a figure known as
"reserve alkalinity" which is the capacity for neutralizing acid formation.
But if motor oil or blowby gases manage to get into the coolant through
some mechanical fault [head gasket failure?], it's pretty much game over.
Silicate compounds are a traditional corrosion-inhibiting protectant additive,
such as found in the canonical "green stuff", but have a tendency to drop out
of solution and form gels or grits after too long inside a cooling system.
This can foul and clog components, wear out water pump impellers and seals
prematurely, and cause all kinds of havoc. So silicates are now less in
favor as additives than they used to be.
Organic acids such as carboxylates tend to form thin barrier layers on metals
and thus have good anti-corrosion properties and generally longer protection
life, but tend to bring down the pH of the mix they're in [but not to truly
Hybrid organic acid formulations, called HOAT, retain a certain amount of the
silicate [or in some cases, phosphate] based corrosion inhibitors and try to
strike a long-life balance between silicate/phosphate and organic acid levels
to achieve the longest protection life for typical metal parts and materials
found in a cooling system. But that still doesn't tell me if Toyota SLLC has
SOME silicates, or NO silicates.
Anything more in-depth than this quick summary, however, is beyond my own
chemical savvy and the references speak to it with far more authority
than I can. The perfect liquid-coolant would be one with the heat-carrying
capacity of water, the liquid-phase stability of ethylene glycol, the
lubricity of light oil, and otherwise be completely inert. News of such a
witch's brew has *not* yet
come to Hahvahd,
so everything we have now is a set of workarounds.
The bottom line is that although coolant formulation is often complex, these
words and terms shouldn't be so mysterious, and the expected lifetimes and
benefits of these different types of coolants are becoming somewhat better
understood by now but usually at an "only use this stuff!" level.
That's still not going to stop your corner service guy from stroking his chin
and going "36,000 miles? You need new coolant" as a way to drum up a little
work, and we need a second opinion. Thus, the question remains of how to
more accurately test what's going on with a given chemistry in coolants of
a given age.