There are several schools of thought when it comes to coolant. Water is the most effective coolant. However, corrosion issues make pure water unrealistic. The use of water with a corrosion inhibitor works for optimum heat transfer, but isn't popular with most. One engine builder suggests 100-percent antifreeze to prevent corrosion and freeze-ups. Although pure ethylene glycol doesn't transfer heat as well as water, it does transfer heat without corrosion issues if you have a high-capacity radiator. There's also Evans non-aqueous coolant, which is used all by itself without water. It is very expensive, but never needs to be replaced.