i dont know what happens if u mix these together.prob not good lol but my point is the gm manual is very mis leading for people who dont know anything about cars.we know to change our coolant before 100000 miles or were gonna have big problems but other people dont know that.gm needs to change that to every 25000 miles to prevent cortly repairs or go back to the green and it would not matter. thers a good article on the different chemicals in green and dex cool.it explains why dexcool gets so corrosive so quick because of thr different chemicals dex cool has.ill try to find it and post it on here.