Have a '03 VY SS 5.7ltr (series 1) and just changed my cooling pump and thermostat, I have had green coolant in since I bought the car and was recommended to switch to the red so I bought some, I flushed out everything as best I could with tap water and then ran some cooling system flush through it and flushed it out with water again, but I am unsure as to how to make sure there is no left over water (or old coolant/flush) lurking in the system before I put the fresh coolant in, or doesn't it matter? I got premix instead of concentrate (too late to exchange it now), wouldn't any water left inside the system dilute the coolant further? I also read that when changing to red from green or vice-versa that one must make sure to completely clean the system out of the old stuff or risk severely lowering the anti-corrosion properties of the fresh coolant... or am i just over thinking it? Also, the overflow tank is very dirty, there is some scale or something built up and flakes of it where coming out of the hose when flushing, would it be a good idea to remove and clean it properly? what would be good to use? Thanks for any help given.