Quote Originally Posted by IC2 View Post
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:

Like I said Dave, to make rust, it takes air. Yes, free O2. Not part of the H20. All Tap water contains a level of entrained O2. And yes, the water pump can cause cavitation in the coolant and actually causes the O2 in the coolant to explode. With 25 years in water and wastewater treatment, I know those are the facts! The catch can thought was just that, a HMmmmmm I wonder moment out loud. Fluids seek their own level so I had a thought flash through the brain.

I know on my car the radiator fill is set into the side of the top tank. The very center of the top tank has always made me wonder how full the closed system is. It looks like your radiator is the same.

I'm not really concerned like I said earlier. The cast iron will probably outlive me and most of my family. But like you I'm wondering what's at the bottom of my block and will have to investigate.