Water and antifreeze. You need to tell us what the issue is first that you are concerned about. If it's over heating, a good cleaning and learning to use the spark and spray needle go a long way. If your radiator is marginal, adding a water pump is ok in my book, I have one. My OP is if you run a water pump adding a thermostat is a good idea. Bottom line, water and antifreeze is all that is needed. The antifreeze also has rust inhibitors.