Why the hatred of anti-freeze?
Anti-freeze is also a corrosion inhibitor and summer coolant.
Every single motor manufacturer in the world puts it in every single car they sell. Millions of motorists worldwide drive their cars all year round without a second thought for what goes on in their engine.
If you can't just fill with water mixed with the correct ratio of a good quality anti-freeze/summer coolant there must be something wrong with your setup. Millions and millions of people use it every day. Why would someone want to NOT use it?
Auto trans fluid in the rad? Not a good idea. Plain water - Plain stupid.
Sorry, but why constantly try and come up with a better idea when the best idea is what is staring you in the face.
Nice clean water. Good quality anti-freeze/summer coolant.
Put it in. Forget about it.
Find something else to tinker with.
Mart.