DEF Math
The owner's manual says my truck has a 5.5 gal DEF tank. I waited until I was down to 1/4 on the gauge, just above the red zone, and added a 2.5 gal box of Blue DEF from Advance Auto. Now the gauge ...
Forum Discussion
I have a DEF gauge on my 2017 Ford but the 2016 only told me it was OK or less than 1/2 of a tank. At less than 1/2 I could add a 2.5 gallon jug. I ran it out of DEF once just to see what would happen. It was extremely annoying because the warnings kept popping up on the dash. Eventually it got to the point that it limited my speed to 50 mph. I kept driving till the final warning indicated the vehicle was out of DEF and that upon shut off the engine would not restart. I had to add 2 jugs before the codes reset and the engine would start. Now that I know running out won't leave me stuck on the side of the road I very very seldom bother to even look at the gauge..... it seems like a tank of DEF lasts a very long time.
