What's in the radiator? If you havent changed it yet, maybe it still has what it originally came with. As far as only using Dex Cool, I've read a ton of guys on here tellin people to flush the system and go with the green stuff. I'm only at 33k miles and havent completely flushed yet. I did replace some to boost my concentration, but what i pulled out was the exact same color and looked as clean as what I put in, so I'm not worried with dexcool.