There is a ton of misinformation on the web about the two types of coolants, specifically Dexcool vs 'Green'.
Summary:
There is nothing inherently 'EVIL' in either of the two antifreezes. There ARE differences in how they need to be maintained and what happens if they are not. Propylene Glycol (Dexcool) is poorly suited for automotive applications but it does and will work for the life of the vehicle if well maintained and not neglected or abused.

Main thing is to NOT leave air in the sealed portion of the system and change it out when it starts turning color or getting murky.

Dexcool, well maintained, has little or nothing to do with LIM gasket failure. That's simply a cheap design. Fel-Pro {kudos!} fixed it {Like they did for asbestos-free Aluminum head/ iron block head gaskets in the nineties} because they have REAL engineers.
To start with, I'm not a chemical engineer but I'm a guy who never accepted 'Conventional wisdom' always wanting to know 'How and why' and I know me some physics, both from reading and observation in real time and over time.


So lets put some common sense to work instead of accepting marketing and PR BS... ahem.. I mean 'myths'

There are three components to a modern automotive coolant
1. Water
2. antifreezing agent
3. additives.. usually to retard corrosion but also surfactants to enhance heat transfer. A 'surfactant' is also called a 'detergent' in other realms.

The combination of the properties of the three result in protection (and, sometimes, destruction) of the systems in which they are contained and there is much more involved than simply moving heat from the engine to the air flowing through the radiator.

Start with the water
Pure water does not conduct electricity. Therefore it is a 'di-electric' substance. However, it takes very little contamination from a water soluble element or compound to make it conductive.. ie; 'ionized'. Chlorine is an ionizer. So is about every other soluble solid.

To make it simple, municipal tap water is a very weak hydrochloric acid. That's why some people only use distilled or de-ionized water (two different processes) in their systems. In reality, the additives in most commercial products counter the acidity expected in tap water.
Obviously it cant hurt to use distilled when adding or mixing, but it also is not a good idea to add baking soda, unless you are a chemist.

Additives:
'Lubricant' - The claim is that key additives 'lubricate and protect from corrosion'. Well.. not so much lubricate.. because there's no need for it. Dishwashers and auto water pumps use the same graphite seal technologies. and many dishwashers go 25 or more years and never leak through that seal.
Some strong chemical pumps also use the graphite seal system and there's no lubrication there, either. But it makes a good selling point. When your water pump starts leaking, it aint the seal, it's the bearing going out and the shaft flopping. If the pump mfrs wanted to, they could avoid that leak by making the graphite seal a little more robust and forgiving but it makes a dang good warning system.
So.. what's there to lubricate? Not much... unless you count 'coating surfaces to prevent corrosion'
Anti-corrosives:
That's where those evil 'silicates' came in. Silicates, if they exist in your coolant are added to the mix to microscopically coat metallic surfaces and protect against galvanic activity. What is 'galvanic'? Well... your car battery for one. And silication works just like 'sulphation' and you know through a little reading that when the plates in your battery 'sulphate', the thing is shot, because it dont galvan so good no more.
Funny thing.. they actually deposit by 'galvanism' otherwise known as 'plating'. Which is the opposite of 'etching'.
But silicates were just one method - and a cheap one - to accomplish that. There are other additives and none are inherently tied to either green or yellow, other than how they react to the given glycol properties.
- sidenote: When green started going 'low silicate' in the mid nineties there were a rash of water pump failures where the pump impeller actually 'disappeared' through galvanic etching. This was due to cheap mfg processes and IIRC, cadmium plating the impeller solved the problem.
Sidenote on galvanism. We know from elementary school experiments like potato and lemon batteries, that dissimilar metals electrically joined by a conductive fluid generate a weak charge. You can also induce electrical eddy currents through molecular friction. Why the impellers gave up. Thus the coolant rushing from an iron environment through a copper or aluminum heat exchanger will corrode more rapidly, all else equal, than one where the fluid is relatively still.

So now we see the real importance of anti-corrosion additives and the types used with the two main components.
And they arent always the same.

Glycol properties:

But that's where we start to see the difference in yellow and green. Contrary to misinfo promulgated by 'experts', Green does not 'wear out'. The additives in it wear out or lose potency.
Being basically lazy, I've had vehicles go about 8 years without a system flush. Simply by checking the Specific gravity and Ph balance.. and fixing the Ph by adding fresh green and Redline Water wetter. I dont recommend that I'm just saying.

And all else equal.. that's where we see the difference in a poorly maintained system.
Air and heat cause Propylene Glycol to generate Lactic Acid.
Perhaps, since Propylene and Ethylene glycols have both been used for a long time, that's why PG wasnt used until the closed system. ie; the overflow bottle was introduced.
We also know that EG has a problem with environmentalist because it's a poison while PG is used to seasonally weatherize drinking water systems. Not that you can drink PG, it's just not a poison, per se.
But Propylene Glycol degrades over time at any rate, where EG is relatively stable.
The main reason to flush and change either is to keep the system operating at max efficiency.
For Dexcool it is imperative because it's not just a matter of flushing rust, it's replacing the degraded antifreezing component which causes corrosion in its own right.


Wikipedia

Cooling Properties:
Also counter to some conventional wisdom {aka BS!}, Glycols do NOT transfer heat nearly as well as plain water. That's why you keep your mix low as possible for your climate. Some 'experts' have claimed glycols help because of their higher boiling points.
False.
The difference is negligible and just MIGHT make up for poorer wetting of the transfer {hot} surfaces. Surface tension is affected by specific gravity among other things, Glycols have a lower specific gravity than water thus carry less heat by volume, and both water and glycols need a 'surfactant' to reduce the 'skin effect'.
The higher boiling point really is a function of the pressure in the system. ie; the radiator cap.

Additives in both types act as surfactants. Redline water wetter has the same additives as coolants without the antifreeze. So if you want to use less than 40 percent glycols, make sure to protect with the water wetter.
It's much more important that the info be right than for me to be right. I aint Rick.

 

Thanks for the detailed work, pettyfog, but Kyle, Gary, and I have all stated the same info here over and over without it sinking in. Those that want to believe the 'evil Dex' myth are not going to be swayed by facts.

I do disagree with the statement "Propylene Glycol (Dexcool) is poorly suited for automotive applications but it does and will work for the life of the vehicle if well maintained and not neglected or abused." It is self-contradictory after the word 'applications'. Any system or fluid will fail if not maintained correctly or if neglected. It's just a matter of time.

I do not want this to become another 'DexCool' thread, we have enough of them already so, unfortunately:
*Thread Closed*