whoops....read like 3 post then just went to the bottem

 

That's what I was talking about whenI said that the antifreeze will coat the inside of the radiator with a thin scale that protects the radiator from corrosion. It is possible that running straight distilled-or even more so deionized water-would result in increased corrosion of the car's cooling system. This goes for copper as well as aluminum radiators. Of course if you've been using antifreeze or tap water over the last 40 years, there is probably enough scale built up on the inside of the cooling system that it will take several drains and refills with at least a few 100 miles of driving in betweenbefore the distilled/deionized water dissolves all of the deposits and starts attacking the metal. Is this effect worse for aluminum? That I don't know of the top of my head. I do know that even stainless steel is susceptible to corrosion from deionized water, it is a highly aggressive substance.

 

Yea the water has been goodeverywhere I have lived, both in SE AZ and SW NM, always ground water, and really clean except for a little calcium.My radiators have always lastedfor at least 12 years, and often more than 20 years, with the exception of the "plastic tank" ones that sometimes break without warning.

This was a longer post, but I lost it to an ASP-500, probably better shorter anyway though.

 

i have a water cooled pc i seen what happens when you dont use distilled water the cooling blocks had build up in them thats the reason i use it in my cars

 

My answer would have to be.... what does my school book teach about it, and here goes.

Engine coolant is actually a mixture of water and antifreeze/coolant. Water alone has a boiling point of 212deg F (100deg C) and a freezing point of 32deg F (0deg C) at sea level. A mixture of 67% antifreeze and 33% water will raise the boiling point of the mixture to 235 F (113C) and lower the freezing point to -92F (-69C). Antifreeze in excess of 67% will actually raise the freezing point of the mixture. The typical recommended mixture is a 50/50 solution of water and antifreeze/coolant.

other then that as long as I have a nice green looking coolant I figure its good enough.

Edit: It also talks about tap water causing hard water deposits due to the minerals in the water, and that you should use distilled water. (same goes with your battery)