Does anyone know if 2 cycle oil goes bad? I use Polaris blue, but I never run the oil tank down low, I just keep adding when needed. My bike's a '99 so it's possible there could still be oil from when it was new mixed in the oil tank. Should I dump it and put in fresh? How often should you change it out?

Unless you have a reason to think it got contaminated I wouldn't worry about it, just keep on adding as you need it and by riding it will blend and make no difference IMO.