Full DEF Tank Mystery Solved

Full DEF Tank Mystery Solved

Several months ago, I wrote about refilling my truck’s Diesel Exhaust Fluid (DEF).  In case you never heard of DEF, it is a liquid that is consumed in small quantities when you drive a newer diesel truck.  DEF is used to lower some types of emissions and is required on all new diesel trucks sold in the USA.  The new trucks will not run without DEF.  Running out of DEF disables the engine.

Spoiler Alert – DEF MPG provided below.

My last diesel truck, a 2001 Ford F-250, was built before DEF and so this new truck is my first experience with DEF.

My goal in tracking DEF usage has been to understand what the truck’s range is so that I can make sure that I never run out of DEF.  Since we plan to travel to Alaska and back next summer, I want to make sure that we don’t run out of DEF on the Alaska Highway where DEF might be hard to come by.

Just a quick recap on what has happened with my DEF so far.

Not Enough DEF To Get Home On
Not Enough DEF To Get Home On

In the middle of my last big trip, outside of Winslow Arizona, the truck reported that I didn’t have enough DEF to get home.  I bought 2.5 gallons of Bue DEF at the Flying J in Winslow.  I was amazed at how quickly you can put DEF in your tank when the tank isn’t full!

Blue DEF Purchase - 2.5 Gallons
Blue DEF Purchase – 2.5 Gallons

This DEF cost $6.40 per gallon which seems high.   It did give me enough DEF to get home on.

Adding 2.5 Gallons DEF - Tank Now Half Full
Adding 2.5 Gallons DEF – Tank Now Half Full

After getting home the next week, I needed to get another oil change and a state inspection for truck license renewal.  I didn’t want the dealer to fill my DEF tank again (and not own up to it).

I went to a Travel Centers of America (TA) truck stop where they have DEF on the truck pumps.

Commercial Truck Pump at TA Truck Stop - Diesel and DEF
Commercial Truck Pump at TA Truck Stop – Diesel and DEF

Not being a commercial truck driver, I was kind of at a disadvantage when I tried to fill at the same pumps used by 18 wheelers.  When I swiped my credit card, the pump told me that I didn’t have authorization to use the pump.  I had to go inside and prepay with my credit card.  I filled both the diesel and DEF tanks but I underestimated the amount I needed to authorize for prepay and ended up running out of money on the first prepay during the DEF fill.  So I went back inside to the fuel desk and put another $20 down on DEF.

When filling at these pumps, the diesel works as expected (except for the business with authorization and having to prepay inside at the fuel desk).  The DEF controls and nozzle are on the right hand side of the front of the pump.

DEF Button Below Credit Card Reader
DEF Button Below Credit Card Reader

When I was ready to fill with DEF, I pushed the big yellow Diesel Exhaust Fluid button.  To the right of the button is this weird semi-transparent sleeve thing I had slide up to reveal the DEF nozzle.

DEF Nozzle Assembly With Cover Slid Out Of The Way
DEF Nozzle Assembly With Cover Slid Out Of The Way

I pulled the nozzle out of the contraption.  The contraption really didn’t want me to extend the hose.  I felt like I was in some kind of cartoon where the hose kept pulling me into the pump.  Holding the nozzle with my right hand and keeping tension on the hose going to the pump with my left, I was able to get the nozzle into my DEF spout and fill it.

The DEF used is displayed in the same display used for diesel.

Diesel and DEF Vended Shown In The Same Display
Diesel and DEF Vended Shown In The Same Display



The DEF MPG measured assuming Jordan Ford in San Antonio did in fact fill my DEF tank in December is…

497 MPG (Miles Per Gallon) DEF

The average Diesel MPG for the same period was…

9.6 MPG (Miles Per Gallon) Diesel

The above numbers represent truck with camper mounted towing Jeep Wrangler over 99% of the miles driven.  The fuel mileage looks horrible.  Looking back on the individual fuel mileage log entries, the worst mileage occurred while driving I-10 and I-8 West from San Antonio toward Parhump, NV.  We had serious headwinds, side winds, dust storms and sandstorms on that portion of our route.   I was also driving fast – from 65 to 75 MPG.  Returning home along I-40 and then down into Lubbock on US highways we had fuel mileage above 10.  Gentle winds and speeds in the 55 to 65 range.

Hope to see you on the road ahead!



Add Your Comments, Questions and Observations

This site uses Akismet to reduce spam. Learn how your comment data is processed.