The bright orange Dexcool coolant used in many General Motors vehicles over the past decade promised to bring extended maintenance - 5 years or 150,000 miles - to cooling systems, but many owners instead found themselves with vehicles that required system flushes, gasket replacement, and even new radiators and heater cores just outside of the vehicle's warranty period. The blame for the problem depends on who you talk to, and the causes include the "stop-leak" pellets added at the factory, contamination with air from system leaks (Dexcool can quickly degrade when exposed to excess oxygen), and improper service that involved added non-Dexcool coolant or tap water to the cooling system.
Whatever the cause of the problem, several lawsuits have been filed in state and federal court by owners who, in many cases, are justified in their anger over the lack of performance by this coolant. A ruling may soon be forthcoming from a judge in East St. Louis, IL, that would result in a set of consolidated suits gaining class-action status - a move that would open up the lawsuits to involve potentially millions of GM customers. For its part, the automaker says that the recommend service interval in the owner's manual is exactly that - a recommendation, and not a warranty guarantee.
For what it's worth, the Autoblog staff has found that Dexcool works just fine in a cooling system that is free of contaminants and leaks, but indeed the stuff will turn into a gooey mess if mixed with anything but distilled water or if exposed to air. Also, those drivers who do not get their vehicles up to normal operating temperatures every trip may want to consider an accelerated coolant maintenance schedule.