When I went to add coolant to an empty overflow tank in my 70 Cutlass (Rocket 350), I noticed two things. First, the lines are marked Add (bottom line) and Full (top line). To what level do I add fluid when the engine is cold. Second, what is the second hose coming from the top of the coolant overflow tank? It's not attached to anything, nor is it long enough to ever have been attached to anything. Is it a vent - should I be concerned? Thanks. - Ken