DEF Age Question

[shertex]

My 2014 E250 Bluetec has a DEF tank that holds 6.5 gallons. I drive the car about 5000 miles per year and that translates into about 2 gallons of DEF per year.

My understanding is that, if properly stored, DEF can last up to two years from manufacture date. But I'm assuming that DEF in the tank will degrade a bit faster. What are the potential adverse effects of having DEF fluid that's a few years old in the tank? I'm wondering if I should periodically drain the tank and put fresh fluid in there.

Maybe I'm worrying unnecessarily....but the SCR system is complicated and repairs can be expensive. I want to do everything I can to ensure its longevity.

Thanks.