There is remarkably little difference between the green
antifreeze and DexCool. Both are ethylene glycol-based. Both require a 50/50 mix with
distilled water. GM claims tap water is suitable for DexCool, but why introduce unnecessary minerals to your engine? The differences rest in the type of corrosion protection each product offers. Green coolant uses a silicate-based corrosion inhibitor that coats the metal. Over time, these inhibitors break down, requiring a coolant flush every 30k miles or so. In an aluminum engine, green coolant does not change color when it breaks down; so many owners have no idea when this has actually occurred until their nice expensive aluminum heads have cracked. In an iron block engine, green coolant will turn reddish-brown with rust when its corrosion inhibitors break down. DexCool (phased in by GM during the 1995 model year), on the other hand, uses an acidic (GM calls it “organic”) corrosion inhibitor that does
not break down over time. However, DexCool does not coat metal components as much as green coolant does, so proper levels must be maintained to ensure corrosion protection. Because corrosion protection does not diminish over time with DexCool, it can be left in the engine much longer than green coolant. While it's disputable whether or not you should leave DexCool in for the 150k miles that GM & Texaco claim,
DexCool should easily be able to stay in the engine for 75k miles, two and a half times that of the green coolant. 75k miles is generally what the average vehicle travels in 5 years, and GM does not recommend leaving DexCool in for longer than 5 years.
