towing def usage | wow!

[steiny93]

Last weekend, put the boat (621 Ranger) behind the wife's denali xl and headed to a lake about 200 miles away (~400 miles round trip).
Near a full tank of fuel and near a full tank of def [didn't need fuel for the trip, entire trip on the tank we started with]

Down the interstate we go
within 100 miles I get a def warning; 1000 miles remaining (not to worry, we only have 300 miles round trip remaining @ def is over 3/4 full per gauge)
on the way back, 100 miles from home; 250 miles def warning (still not to worry, we have over double the range @ def is 1 bar below 1/2 per gauge)
20 miles out; it gives the def low, limp mode soon message; gauge goes all the way to empty and turns red

Is everyone else experiencing this when towing?
Dealer again states, yep, as expected, just carry def with you when you tow or stop for def between diesel fills.

My ecoDiesel, Cummins, normal dmax all can go significantly further than a single diesel tank on their def capacity, this baby dmax seems off.

 

[Stbentoak]

It is worth at least reviewing this with your delaerships Diesel Mechanic. Certainly seems excessive but these gages are in exacting at best. You may think you were near full and by volume you could have been at 70%. But yes, they use more than HD vehicles and yes this still seems like a lot if it was over, say 5 gal.
I dump a 2.5 in at every oil change without towing. That regiment has never left me with low DEF, nor ever got old....

 

[martinajm]

It seems high for that small of a payload, but not by an order of magnitude. The range calculations are not exact by any means...

 

[DuraYuk]

The DEF range adjusts based on demand. Similar to you miles remaining for gas. Because the volume is less the spread can seem more drastic.

 

[StephenPT]

Just got back from towing a 5K travel trailer - about 1300 miles round trip to Lake Tahoe. Left with 100% on the DEF gauge both verified with Bank I-Dash and the center cluster gauge. After about 600 miles of driving I got a "DEF Range 1000 miles" notification. Dismissed it and didn't see the message again as we took day trips to different places in the area. Got a jug of DEF at Walmart in Carson City before we left, dumped 2.5gal in and then just before we got home I got the 1000 mile range notification. Might have been able to do the whole trip on one tank, but it was easy to top it off before we headed home.

FWIW - I don't go much above 62mph while towing unless I'm passing a semi. Also, I have only ever used Walmart DEF since day one. At $9/jug you can't beat it.

 

[Scarey]

If my math is right you used about 5g def in 1300 miles towing?

 

[swathdiver]

Soon fellas, you'll be able to get rid of that garbage.

 

[PPK_]

I have duramax SLT 2025 truck ... normal conditions driving it uses just a little def. maybe 2k miles empties the 5 gal tank. towing is a different matter. i used the full tank and two 2.5 gallon defs. it is terrible. DEF is $15 at 2.5 gallon at walmart.. (not walmart brand) and you put 4x15 bucks a gallon on top of $3.40 a gallon fuel.. not good.

i wish had a 6.2.

The diesel will pull a trailer (25') but it is so expensive to tow.. and the mileage while towing is about 10 mpg. not very good either.

The 3.0 duramax is not a good tower. not at all.

 

[Stbentoak]

I have duramax SLT 2025 truck ... normal conditions driving it uses just a little def. maybe 2k miles empties the 5 gal tank. towing is a different matter. i used the full tank and two 2.5 gallon defs. it is terrible. DEF is $15 at 2.5 gallon at walmart.. (not walmart brand) and you put 4x15 bucks a gallon on top of $3.40 a gallon fuel.. not good.

i wish had a 6.2.

The diesel will pull a trailer (25') but it is so expensive to tow.. and the mileage while towing is about 10 mpg. not very good either.

The 3.0 duramax is not a good tower. not at all.

That's not logical. I can go at least 10,000 miles on a full tank of DEF unloaded. I dumped a 2.5 in every oil change and it always keeps me around the half full mark plus or minus.
That was on my 21 LM2. Not seeing any different trend on my 25 LZ0.....

 

[StephenPT]

I have duramax SLT 2025 truck ... normal conditions driving it uses just a little def. maybe 2k miles empties the 5 gal tank. towing is a different matter. i used the full tank and two 2.5 gallon defs. it is terrible. DEF is $15 at 2.5 gallon at walmart.. (not walmart brand) and you put 4x15 bucks a gallon on top of $3.40 a gallon fuel.. not good.

i wish had a 6.2.

The diesel will pull a trailer (25') but it is so expensive to tow.. and the mileage while towing is about 10 mpg. not very good either.

The 3.0 duramax is not a good tower. not at all.

What speed are you towing at? I tow a 25' Keystone Passport. On the scale I'm at exactly 5K. Towing through the passes in the Oregon region I get ~12mpg. Towing in the flat regions (up and down I-5) I'm getting 15mpg. Cruise is set at 62mph.

The low end torque of the 3.0 Duramax means the engine doesn't have to scream to get over a pass. Usually it downshifts to 7th or maybe 6th gear to get over a mountain pass. Cruising on flat terrain it lives in 9th gear and doesn't deviate until it has a hill to push. (Using tow haul mode)

 

[StephenPT]

If my math is right you used about 5g def in 1300 miles towing?

I'd say pretty close to that. My Bank I-Dash says I have 73% remaining. While towing that's about where it gives the 1K mile remaining warning. It's certainly a lot more DEF usage than driving unloaded, but it's worth it for the overall experience of towing with a diesel.

 

[dbphillips]

Should be 2-3% DEF:diesel.

I don't care if the GM nannies limit me to 65 towing, so would be happy to let it threaten for 500 miles, then I guess another 500 miles at 65 mph. _Except_ they prevent access to critical information on the dash, like current fuel economy, transmission temperature, tire pressure. Definitely need a way to disable that prevention. It's really a safety issue.

 

[JayceeP]

I have duramax SLT 2025 truck ... normal conditions driving it uses just a little def. maybe 2k miles empties the 5 gal tank. towing is a different matter. i used the full tank and two 2.5 gallon defs. it is terrible. DEF is $15 at 2.5 gallon at walmart.. (not walmart brand) and you put 4x15 bucks a gallon on top of $3.40 a gallon fuel.. not good.

i wish had a 6.2.

The diesel will pull a trailer (25') but it is so expensive to tow.. and the mileage while towing is about 10 mpg. not very good either.

The 3.0 duramax is not a good tower. not at all.

I got 11 months, and about 8,000 miles out of my tank of DEF. I filled it in Aug 2024 and added 2 jugs in July 2025. No towing but lots of highway with decent sized hills. Also, Nova Scotia gets messy winter weather.

I’m in a 2024 Yukon XL SLT.

 

[Stbentoak]

I have duramax SLT 2025 truck ... normal conditions driving it uses just a little def. maybe 2k miles empties the 5 gal tank. towing is a different matter. i used the full tank and two 2.5 gallon defs. it is terrible. DEF is $15 at 2.5 gallon at walmart.. (not walmart brand) and you put 4x15 bucks a gallon on top of $3.40 a gallon fuel.. not good.

i wish had a 6.2.

The diesel will pull a trailer (25') but it is so expensive to tow.. and the mileage while towing is about 10 mpg. not very good either.

The 3.0 duramax is not a good tower. not at all.

You seriously should sell it then. There are a million people out there that would love to unload their 6.2's right now and have a Duramax. You could even probably find a dealership that would trade you even up. Duramax's are far more valuable since this 6.2 debacle.

 

[PPK_]

You seriously should sell it then. There are a million people out there that would love to unload their 6.2's right now and have a Duramax. You could even probably find a dealership that would trade you even up. Duramax's are far more valuable since this 6.2 debacle.

Def… is used a different rates. Cruising 75 mph on the hwy is a use 1% of fuel.. you load up the truck with a 6k lb trailer and the engine uses a lot more. 3%?

The truck is not a good tower. It just fine cruising around. The truck also seems to be in regen mode more when towing.

As far as trading… not. I gave 54k for my slt truck.. i also have a 24 slt yukon… i am getting where i hate to pay taxes on these things… it is what it is.

 

[dwhittler]

I have duramax SLT 2025 truck ... normal conditions driving it uses just a little def. maybe 2k miles empties the 5 gal tank. towing is a different matter. i used the full tank and two 2.5 gallon defs. it is terrible. DEF is $15 at 2.5 gallon at walmart.. (not walmart brand) and you put 4x15 bucks a gallon on top of $3.40 a gallon fuel.. not good.

i wish had a 6.2.

The diesel will pull a trailer (25') but it is so expensive to tow.. and the mileage while towing is about 10 mpg. not very good either.

The 3.0 duramax is not a good tower. not at all.

I owned a new 2023 Yukon Denali 6.2 until GMC recalled it. Now I have a 2025 Yukon AT4 ultimate 3.0. Just got back from towing my 5-6K pound cargo trailer from Houston to Albuquerque. On the way there, going uphill a lot of the time, foot to the floor to maintain 70 mph some of the time, got about 9 mpg, used about 22 gallons of DEF. The 3.0 would consistently go into limp mode with the DEF guage showing about 3/4 full, never able to get more than about 2 gallons of DEF in the tank. On the way back, going down hill a lot of the time, got about 13 mpg, never added any more DEF. Two weeks later, driving around town I have filled the diesel tank once, still have not added any more DEF, still shows full on the guage, the pop up message telling me I have over 4000 miles of DEF remaining, getting about 22 mpg. Note that out in the middle of nowhere (west Texas, east New Mexico) the few gas stations or auto parts stores that even have DEF charge an average of about $23 for 2.5 gallons.