Quote Originally Posted by 34_40 View Post
Actually, to make rust, you need AIR. Water alone will not make rust. An example would be deep sea wrecks that are wooden and are still there centuries later. Even wrecks in the great lakes are very well preserved because the water is very cold and deep with low oxygen contents.

I'm assuming that your radiator elevation rises (when hot) and falls (when cold). It's this headspace where the falling coolant can trap air into the coolant which gets left in the block. The air/water combo is what's attacking the bare metal. I'm wondering if the "catch-can" is to low and allowing an air pocket to develop. And now that you mention it, I'm wondering about my own car. I'm not worried as the cast iron will be along time before a catastrophic failure, but still.

Great topic Dave! Now my mind is curious!
What you are describing, Mike, is free oxygen, that is molecules of entrained oxygen(air!) that is not part of the H2O combination. In the case of an automobile cooling system, it's a closed system, opened only when you check the coolant level or boil some of it into the overflow vessel(15psig). It can also happen if the water pump cavitates - but that usually wont happen unless the water level has gotten too low Boiling has happened only once to me - two years ago and that was because I didn't have the fan wired correctly and was fixed immediately after cool down. As far as my overflow/catch can - it's pretty high plus a good size compared to many. I did move it from one side to the other recently, but it's at about the same height.

Another plus with using antifreeze is that it does contain anti corrosives, water wetting agents, raises the boiling point a few degrees.

This is my coolant recovery system: