Originally Posted by Shane Stroud
Pull out an old (way old) line. Lay it out. Inspect it. Clean it. Inspect it. Dress it. Inspect it. Spool it. Inspect it. Fish it. Inspect it. That's the only way to know for sure. Oh, did I mention that you should really inspect it? As long as it hasn't cracked or otherwise degraded, it's a fishable line.
I've been through that a few times. Finding out whether or not an old, forgotten line works is a true win-win situation. Even if it doesn't work well for you, it doesn't matter. You still get to fish. And we all know the worst day fishing is better than the best day working.
Pretty much right on the money. I would add that the first post about stretching line is true too. Sadly as much as I love my conventional spooled Hardy reels, large arbors do have one distinct advantage, line will definitely last longer when spoiled in larger coils. This may be the one rub of five year old fly line stored on reels. Most Fly lines will hold up well without wear, it's going thru the rod guides that wears them out.
But if they were stored wet, or not in a place with that is cool and dry you may have issues with the coating degrading or the core rotting. The only way to find out is to test them and apply some tension to them.