Change distilled water coolant?

[schnellman]

You should be using a 50/50 blend of water and coolant year 'round. The coolant has additives that not only prevent freezing and raise the boiling point, but provide rust protection and lubrication. Porsche recommends its own (expensive) brand of coolant. However, any good brand such as Prestone, will do. And, leaving the system dry is not a good idea.