[laverdur]

Until a couple weeks ago, I always bought my DEF from the Ford dealer. Yes, I might have been paying a little more for it than from another source but I knew that they rotated stock frequently. What I have learned is that DEF has a shelf life. That shelf life is shortened by exposure to sunlight and heat. Until my last trip my experience when towing was about 3,500 miles to a tank of DEF. That includes use of some DEF that had not been stored under the best of conditions. On my most recent trip I got 4,700 miles on a tank of DEF. That included 2,900 miles of heavy towing, 400 miles of light towing and the remainder local in town, non-towing mileage. In this most recent case, the DEF was almost empty when I filled it with new DEF from the dealer. As noted in the first sentence of this post, the reason I bought non-dealer DEF was because I needed to top up the tank and the nearest dealer was 50 away. I bought a jug at a truck stop and used a little of it to top the tank. No problems so far. I'll use the rest of that jug and then go back to DEF from the dealer.