Dex Antifreeze/Stubborn Radiator Cap?
 

I have a 1997 Chevy Van that has some type of endurance antifreeze in it that doesn't have to be changed for 5 years or 150,000 miles. The sign on the radiator reservoir says it is Dex antifreeze and to consult the owners manual. I bought it used and it doesn't have an owners manual.

Does anyone know what this stuff is, whether it is any good, and where I would buy it (Advance Auto didn't have a clue & I don't see it at Walmart)?

Also, this thing has a round plastic radiator cap that I can't get off...I can turn it about a quarter turn, but you can't push down and turn it the rest of the way like on other radiators caps. Anyone know what I'm doing wrong?:confused:

Any late model Chevy Van (>1996) Owners out there can give me a hand???