On lightly modded cars, start with a small nozzle if you run the brew or washer fluid. Most cars with a 3.4 would probably take a DO3 and be happy. Heavier modded cars will take a DO5 or equal most likely.
The more potent the mix, the more you're gonna need. Remember, you're just trying to quench the KR, not drown it. It is still water mixed in there, and too much will be like running on a 100% humidity day. Don't over do it, but be careful.