Lots of good info here Dennis: http://www.no-rosion.com/tech_coolant.htm No-rosion says distilled water should not be used as straight water coolant, because it can cause damage to system metals. The reason has to do with how distilled water is created. During the distillation process, water is vaporized into its gaseous phase, so all impurities are left behind. These impurities include a number of minerals, including calcium and magnesium, the two components of hardness. The water is then condensed back into its liquid phase, so the resulting liquid is pure water. In fact, some of the purest water on earth. The problem is that distillation strips impurities from water, resulting in water molecules that are electrochemically imbalanced. So distilled water will actually strip electrons from the metals in a cooling system as it attempts to rebalance itself electrochemically. This can result in damage to metals in a cooling system. Using distilled water in combination with 50% antifreeze effectively cuts the amount of distilled water in half. By compounding with glycol, it will not cause damage to metals in a cooling system. For this reason, it is safe to use distilled water in a 50/50 mix. Barry ___________________________________________________________________________ Dennis Valdez sjcarguy60 at yahoo.com Mon Aug 15 20:02:31 EDT 2016 Interesting topic. I have a fluidyne radiator in my car installed by the PO several years ago. No leaks at all at this point. I bought a zinc anode and plan on putting it in on the next flush:Here is the one I bought from Amazon Are most people using distilled water mixed 50/50 with coolant? I seem to recall reading either on the PI forum or in the newsletter that tap water is better. Dennis