I have a 5.3 vortex flex. I had to drain the radiator and engine of its coolant. With some research I found I should stick with gm dex cool coolant. What I couldn't find, even after looking in the owners manual is how I should use...? 2 gallons of rex with 2 gallons of drinkable water? Or 3 of each... Maybe I should just eye it? Trying to save as much cash as possible.