Hey all, we are on our spring migration home from Port Aransas TX to NW MT.
Stopped in Lubbock for a couple days.
My DEF never came off FULL when not towing in Port A, put 1800 miles on her.
Topped it off and drove 550 miles to Lubbock, somewhat of a head wind at times 20 mph. Threw my MPG out the door, 8.9 over 550 miles doing 65 mph.
What was concerning was the DEF usage, A half tank (assuming that 3.75 gallons?) to travel 550 miles. Normal?

2021 F350 Lariat Crew Cab DRW 6.7L Diesel pulling 14,000 35 ft Grand Design Solitude. 2 pax and 2 labs.

 

DEF usage is directly related to the amount of fuel burned. Burn more fuel, use more DEF.

 

My understanding is that the exhaust gases are hotter when towing and more DEF is required for managing what comes out the tailpipe.

Mine uses more DEF when towing.

 

With my gas truck I'm pretty **** about keeping records for tax purposes but with the '16' 6.7 I never recorded the mileage from def fill to the next fill, I'll check the dash screen occasionally and when it show less than 1/2 I'll purchase 5 gallons and keep topping off the tank till the second jug is gone eventually. Truck has 53k on it of which 38k is towing the 5th wheel. I don't think I've purchased more than 20 gallons of def in a year (If memory is recalling it correctly). The last def I purchase was in November coming out of CO.
The truck has never gone through a full tank of fuel without the 5th wheel on it towing other than when I bought the truck in MO and drove it to TX in Jan of 2016.

I'll have to keep a record this year of mileage for dsl & def when I pull out of AZ and head north for our travels till the return south next winter.

 

If you don't tow, you may very well be able to make a tank of DEF last the entire span between oil changes. I know folks you putter around in their trucks and never have to add DEF. Their dealer takes care of it for them when they change the oil.

On the other hand, if you are towing, and especially if the trailer is heavy or tall, at high speeds, in hilly terrain, and/or into a stiff headwind, you will consume a lot of DEF. DEF usage goes up as exhaust gas temperatures rise, and temperatures rise as the engine works harder.

 

it is the towing as mentioned. 3K for my 2021 F450 between fills is the average.

Because of the usage, I have the def gauge on the dash and not the boost gauge

I wait until it gets around 500 to empty then fill.

 

I've thought about making this change as well. Boost is cool but it's not a very useful gauge.

 

I have an SCT programmer set to tow and get over 3K on a tank of DEF, wen it says 500 miles left I still can not get in a 2.5 gallon box. I quit using the box DEF and now fill at truck stops when I fuel using the ESF card. That boost gauge will let you know your having and engine issue, no boost = no power.

 

I think the newer trucks have larger DEF tanks and I know they use more DEF. Folks saw a good jump in usage from 2019 to 2020.

 

Thanks fellas.
I estimated I used 8 gallons going 2200 miles, 1/3 into head winds.

 

Hi OP, on my 2024 when I am using it for errands, my DEF lasts forever. When I towed my 5th wheel for the first time, I was enlightened about the amount of DEF I was using in the HO 6.7L. I was hauling around those cardboard/plastic jugs in the rear. It added weight to my truck that I did not want to pay for or add to my hitch weight as I wasn't gonna leave the wife on the side of the road, ha ha. Then, I discovered DEF at the pump. Way too awesome.

So, if you are worried you are not using enough DEF or your gauge is bad, find a truck stop with DEF at the pump and fill er up. That way you don't have to leave an open container in the garage. One bit of advice when doing that, DO NOT attempt to top it off after it clicks. Yep, I got to clean the fluid off the truck. I agree that DEF is DEF and a truck stop is most likely going to be more fresh than Costco or Wallyworldmart. Much cheaper in bulk too. The most I paid in 2024 was about $4/gallon.

As a fire engine Engineer for many years, I got to smell the diesel and bad stuff way too much for most of my career. Then our latest fire engines arrived with the DEF system. Experience told me to don't trust the clean exhaust. So, I tested the exhaust for CO and there was little to nothing there. It was very clean exhaust and I felt safer knowing that. What I am trying to share is that there are so many DEF haters that do not understand what they are exposed to in exhaust until later in life. Yes, it costs more than an NO-DEF system, but isn't you and your family more important?

 

I figure I use about 1 gallon of DEF every 1000 miles not towing, and about 1 gallon every 800 miles when towing on my 2017 F350.

 

Same.

No issues around my Kubota with a DEF, but working around somebody else's old John Deere that's pre-emissions gives me a headache. My 2014 had a few emissions issues, one resulted in getting stuck half way across the country before we were scheduled to come home. Thankfully the derate warning came on the day before we were to leave, rather than mid journey. I wouldn't mind it much if it gave you a 500 mile warning, but 50 or 100 miles just sucks when you are a long ways from home.

On my 2014 I'd always wait until the 500 miles of DEF left warning came on & then some so I could fit a full jug in. Otherwise you could only fit a partial jug in. I think my 2024 DEF tank is bigger. At least it has an actual gauge on it rather than merely an idiot light. DEF at the pump is nicer for filling things up. I had issues being able to get authorized at the pump for it at some truck stops though.

You use WAY more DEF working the engine & pulling than you do using it as a commuter.

 

Not towing, with 60 MPH average I get around 800 miles to the gallon of DEF. Truck averages about 17 MPG fuel. The 2019 hardly used any DEF in daily driving, only when towing. I haven't towed yet, but I suspect I will be filling DEF every time I stop for fuel.