RVers with diesel powered motorhomes know all too well that the unwritten rule that says whenever you are far from anywhere, in the middle of nowhere, that is when your warning light pops on saying your engine is low on Diesel Exhaust Fluid.
There seems to be, at least from our experience with several diesel RVs, no good indication when you will run out. Sometimes, I get close to 10,000 miles. Other times, more like 7,000. I suspect it has to do with driving conditions. Running long and hot, climbing a lot of mountains and driving hard over multiple days seems to drain the DEF levels faster.
Anyway, hence this quick tip that I follow: Always travel with a spare jug of DEF.
Fortunately, DEF is easier to find now that it was several years ago. Most fuel stations carry it. But sometimes, as in my last DEF fill-up in very rural North Carolina, I had to go from station to staton until finally being directed to an auto parts store.
Bottom line for me: I always have a spare jug with me. As I said in the video, I buy one to put in the RV and one to put in the back of the RV for the day when the current one runs out. Also, my DEF is always topped off when I take the RV in for service every 10,000 miles. But by carrying an extra jug of the stuff, I have one less thing to deal with on long trips.
There's always that spare jug in back.
Like a replacement serpentine belt and spare fuses, carrying a supply of DEF just makes good sense.