With any fluid used in the modern engine or vehicle, the issues surrounding its performance characteristics and/or operational conditions is a complex subject.
Coolant, seemingly a simple fluid, is in fact a complex issue onto itself. To perform upto the expectations of the engine engineers, a modern coolant must meet a wide range of performance characteristics.
Ethylene glycol, the base for nearly all coolants today, is of itself caustic to metals (ever wondered why anti-freeze has never been available in a metal can?), so there have been a number of chemical additives included to reduce this particular problem. In addition these same additives also reduce the problem of electrolysis (dissimilar metals in an acid equal a battery, and years ago it was common for an automotive technician to use a volt meter to calculate the level of electrolysis in a vehicle's cooling system). Another concern is that the coolant have excellent thermal absorption characteristics, so the need for a wetting agent is important to reduce the coolant's surface tension. And then there's anti-foaming agents needed, to keep the coolant from foaming, thus reducing its thermal absorption performance. There's also the rust inhibitors, water pump lubrication additives, and the requirement of balanced pH factors.
Adding to this, Texaco developed and patented their new (new in 1995) coolant with the trade name, Dexcool® and General Motors agreed to use this coolant type exclusively (except for Saturn and diesels initially). Its easy to assume that Dexcool® is the same as any of the so-called "extended-life" coolants, referring to the comment of "..Dexcool® and its clones...", but the technology behind Dexcool® is radically different than just removing the silicates & phosphates in coolant, then calling it an Extended-Life coolant. The base inhibitor package in Dexcool® is a di-acid enzyme (a living organism from an abstract point of view) that bonds to the surface area of your cooling system, forming a barrier between the surface of an engine's cooling system and the ethylene glycol/water mixture.
Another concern is that conventional coolants (green or asian red), new and on the shelf, normally have a pH of 6.5 to 7.5, while Dexcool® typically has a pH of 9.5 to 10.0, partially answering the question as to why Dexcool® has a shelf-life of 5 years, where conventional coolants are limited to 6 to 12 months, before the additive package needs to be boasted.
It should be stated that Dexcool® is an excellent coolant, but there are some conditions or problems that have become apparent since its use beginning in 1996. General Motors started by stating (in the owner's manuals of all GM products using Dexcool®) that the coolant was good for 5 years or 100,000 miles (they later changed the mileage to 150,000 in response to Ford's claim of 7 years and 150,000 miles for their extended life coolant called "Ford Orange"). Where GM said 5 years service life, Texaco stated "up to" 5 years in service. There's no question that Dexcool® is generally good for a longer period of time than conventional coolants, but even Dexcool® will eventually become contaminated with insoluble metals. Where conventional coolants generally need to be flushed every 18 to 24 months, Dexcool® should be flushed every 24 to 36 months or so.
The biggest problems associated to Dexcool® are several, the most noteable being that the average vehicle owner has confused "extended-life" with "maintenance free"! The first problem noted by the dealer's service departments, has been the so-called "Mississippi Mud Syndrome", which was determined to be primarily caused by the vehicle owner allowing their vehicle's coolant level to drop, thus exposing their cooling system's surface to the atomsphere (oxygen, silicates, and phosphates are toxic to the di-acid enzymes used in Dexcool®) and rust immediately is formed and contaminates the coolant, giving it that rusty mud color.
Secondly, Dexcool® has proven to be somewhat corrosive to various components, if left in a vehicle for over 36 months or so, particularily with the water pump, radiator, and intake manifold gasket. Because the warranty for these components ends at 36 months and/or 36,000 miles, a class action lawsuit has currently been filed against General Motors over their use of this coolant. It is my understanding that the suit was prompted by the California Department of Consumer Affairs, due to the high number of consumer compliants they've received over the issue of coolant system repairs needed on GM products, after the warranty of 36,000 miles and before the vehicle has reached 100,000 or 150,000 miles, as stated in a GM vehicle's owners manual.
Micky_M kindly provided a link to Lubegard, where some comparison charts are located. The comparison charts are fine, but Lubegard, Redline, and the other products shown there are generally just consumer level products, though I will admit, based on the ASTM test results provided, that Lubegard's "Kool-It" appears to be superior to some of the commercial products I'm acquainted with (specifially Wynn's, MOC, and JB commercial). The ASTM test that's missing, that directly relates to providing corrosion resistance in Dexcool®, is the ASTM D-2809 test. Here BG SuperCool® is very high rated and I would be curious to see how Lubegard Kool-It performs here.
In the past, as a consumer level product, I have noted that Lubegard's products are generally okay, as testing has shown, but I find that their marketing claims to be so misleading and erroneous to really make me wonder about them. For example, they market an ATF additive that they claim will "convert" Mercon III/IV into Mercon V, which is a neat trick considering that Mercon III/IV are petroleum based ATFs, while Mercon V is a synthetic based ATF! They also claim that their ATF additive is OEM approved, but the fact is that the base chemistry they use is OEM approved and not their product specifically.
