Ethylene Glycol antifreeze needs to have some water in the mix to work properly. It is neither a good coolant nor an effective antifreeze if it's used straight. Never run more than a 70% concentration of antifreeze, which has a freeze point of around 60 below zero F. Straight antifreeze without water mixed with it starts to get a little slushy at 13 degrees ABOVE zero. The standard 50/50 mix freezes at -37 degrees, and also is a good heat transfer medium. Unless you're running your truck somewhere like Fairbanks Alaska, there's not much need to run stronger than a 50/50 mix. Installing 2 gallons of straight antifreeze and topping the system off with water will result in a 50% mix, or slightly stronger. Any water you can drink will be fine in a cooling system. Distilled or demineralized water is ridiculously unnecessary.
Jerry
