Scoobydann --
You probably hold the record for not ever changing your Antifreeze, and your radiator, heater, and engine block have not imploded.
What these new Antifreeze formulations do, besides keeping the water from freezing, is help the mixture in there not turn into acids after it gets old, that attack the soft metals in the radiator, engine block, etc., and render your engine to a dying or dead condition.
The old antifreeze formulas used to be only good for a year or so, before they turned into that acidic product that went amok inside your cooling system. It also forms a quantity of sludge like stuff that in some cases, will plug up the radiator cores and cause problems.
Except for scoobydann, who has the only vehicle in the world that has not been affected.
In my opinion, it would always be good to dump that stuff out sooner than you, scoobydann; so glad you are not having problems - you might want to go buy a Lottery ticket, you lucky guy you !
DC - you can do what you are doing and it should be fine. They do sell antifreeze testers that you can use to see how its going in there.
You would want to take your sample from the overflow tank if possible, so you dont depressurize the cooling system, but if you cant, you can still take it out of the radiator - just make sure the engine and radiator are cooled down completely.
Dan F