You might want to use an radiator flush product usually a few times before you do your final solution. The rust is sometimes hard to eliminate if it has been there for a while.

 Flush it all out  + Radiator Block + heater core too!

Replace with Distilled water + Water Wetter + A splash or few of Antifreeze.  Whole system holds about one gallon.

Your location in the south, you do not require 'freeze proofing" your engine with antifreeze. Antifreeze inhibits heat extraction so keep the antifreeze light in your mixture. 20-30 % antifreeze to water = Consider the antifreeze a good lubricant + anti rust agent...  Water wetter  is a product to help water + heat extraction = be sure to use it.

Hello everyone, live here in Savannah Ga. and bought a 1990 998cc Mini a few months ago and about to flush the radiator etc. Looks like it has rusty old water in it now. When im done, just curious what brand and % of water and antifreeze most people use in these little guys. Thanks much.