Join Date: Nov 2013
Location: SoCal & SoFlo
Thanked 715 Times in 475 Posts
DEF tank is 5.5 gal. When close to "full", I've gone upwards of 3k miles before the gauge even moves. I've added a 2.5 gal jug when it was showing around 3/4 full without it sounding like it was topped off. Perhaps it was a case like Lins stated in post #2.
2014 Granite Crystal Metallic 3500 - 6.7, 4x4, CC, SRW, 3:42, 68RFE, LB, Tradesman -130k miles and going
2005 White 2500 - 5.9 HO, 4x2, CC, SRW, 3:42, 48RE, LB, SLT - 200,000 miles and going.