I have an opened jug of DEF dated July 2019. Can't tell if that is a manufactured date or an expiration date. Any ideas? Or should I just breakdown, dump it and buy a fresh jug?
It’s probably OK, but you can get on Amazon and buy an inexpensive refractometer that will tell you if it still has the correct 32.5% urea. Some refractometers can also check multiple fluids, like antifreeze, windshield washer fluid, DEF, and battery acid.