I suggest you stay with Dex-Cool but only because it had Dex-Cool in it and mixing Dex-Cool with the green stuff has the potential to cause corrosion issues. Even if you flush the cooling system it will be nearly impossible to remove all of the Dex-Cool chemicals from the system and there are warnings about mixing Dex-Cool with the green stuff because of chemical reactions which causes corrosion issues. But I don't trust the 5-year/100,000 mile Dex-Cool change interval. I won't trust any antifreeze beyond 3 years or 30,000 miles. It just becomes too acidic. A pH meter or pH paper will verify that.