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
The composition of DEF is spelled out in federal regulations. There is no allowance for any “secret sauce” and the allowed two components are among the cheapest compounds known to mankind. The only difference between brands is profit margin, packaging, and age/storage conditions (which are more a function of where you buy it). The $2 a gallon stuff at truck stops is your best bet on all counts and is plenty profitable for all involved.
