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DEF Diesel Emission Fluid FAQ - if you own a diesel truck you should read this.


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I thought I was fairly knowledgeable about DEF, but I learned a few important things, like don’t store a spare gallon long term in more than 85 degrees or it will degrade. Here are a few interesting facts.

“the typical average light duty truck will consume 2-3 gallons of DEF per 800 miles. However, most new trucks with an average miles per gallon rating of 20+mpg will go roughly 8,000-10,000 miles on a tank full (10 gallons) of DPF. Each truck is different, 

The only cons to DEF include the additional upfront cost to the truck, added nominal weight and some additional room to store an extra gallon of the fluid. The pros are better fuel economy, increased horsepower, more optimized combustion, fewer regenerations issues, less wear on the engine and in addition it only releases nitrogen and water vapor into the air.

Manufacturers have found that engines containing SCR technology oftentimes get better fuel mileage compared with other smog reduction internal systems. Fuel mixed in with the SCR finds an added source of elements to burn. Fuel mileage can be improved by as much as 5%-7%”

https://www.capitalremanexchange.com/20-facts-you-need-to-know-about-diesel-exhaust-fluid-def/

Sort of related: https://www.rvtravel.com/good-news-def-head-alternatives-coming/

None of this makes me want to buy a diesel truck….😳

John Davies

Spokane WA

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"Mouse":  2017 Legacy Elite II NARV (Not An RV) Two Beds, Hull Number 218, See my HOW TO threads: https://olivertraveltrailers.com/topic/john-e-davies-how-to-threads-and-tech-articles-links/

Tow Vehicle: 2013 Land Cruiser 200, 33" LT tires, airbags, Safari snorkel.

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The new Jeep Gladiator EcoDiesel has a 5 gal. DEF tank and Jeep says the 5 gals. of DEF should last for 10,000 miles, or per oil change. Now I'm sure all will very somewhat, but that sounds pretty reasonable to my and the cost is very little in the scheme of things. 

trainman

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Elite II, Twin Bed, Hull #489, 2019 RAM 1500, 5.7 Hemi, 4X4, Crew Cab, 5'7" bed, Towing Package, 3.92 Gears.

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Since the DEF consumption rate is proportional to fuel burned, if you are towing an Ollie and getting say 16 to 18 mpg, you will be burning, almost twice as much DEF. I would appreciate hearing fuel and DEF consumption numbers from owners here, towing and not towing.

And have you ever NOT been able to find some when you needed it? Ever had your engine go into limp mode? How did you deal,with that?

Thanks.

John Davies

Spokane WA

  • Like 1

"Mouse":  2017 Legacy Elite II NARV (Not An RV) Two Beds, Hull Number 218, See my HOW TO threads: https://olivertraveltrailers.com/topic/john-e-davies-how-to-threads-and-tech-articles-links/

Tow Vehicle: 2013 Land Cruiser 200, 33" LT tires, airbags, Safari snorkel.

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We love our GMC turbodiesel, and dealing with DEF is no problem.  Initially, I kept a backup container in the bed.  I soon learned that many of the major truck stops have DEF right at the pumps, and that is far more convenient, saves space in the bed, and keeps me from one more thing to purchase at Walmart.  It may be a little more expensive at the pump; however, it is worth it to me.  

I monitor the DEF level and never let it get much below half.  Never have I had a problem locating it, but I recommend keeping a close eye on it.  My truck gives a message when I have 1000 miles of DEF remaining.

To me, cost is incidental.

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2021 Legacy Elite II  Twin Beds   "R-Villa" ~ Hull #803 

2021 GMC Denali HD, 6.6 L Duramax Turbo-Diesel, 10-speed Allison

ALARILINIAKYMNMSMOMTOHSDTNWIWYsm.jpg

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On 6/25/2022 at 1:23 PM, John E Davies said:

Since the DEF consumption rate is proportional to fuel burned, if you are towing an Ollie and getting say 16 to 18 mpg, you will be burning, almost twice as much DEF. I would appreciate hearing fuel and DEF consumption numbers from owners here, towing and not towing.

And have you ever NOT been able to find some when you needed it? Ever had your engine go into limp mode? How did you deal,with that?

Thanks.

John Davies

Spokane WA

Not sure about all the tech conversations. Never had a problem with the DEF fluid. My new GMC has a level gauge full to empty instead of a percentage of use, which makes it much easier to know when to add fluid. Adding fluid is usually 3-5000 miles of use, or every oil change. My mileage has increased to 16-18mpg  towing the Oliver. only have  3,000 miles on the truck. I expect this average to go higher once the engine breaks in. There also has been  a big increase in tow capacity 18,000 vs 13,500 on my 2017 HD diesel I thought my 2017 highcountry Duramax was over kill. 🤯 The comfort and safety level of the GMC with the diesel is worth putting in DEF fluid not happy about the fuel prices, who is? Still couldn’t be more happier with the choice of a diesel tow vehicle. 😎 you could also import this to Trainman’s post on tow vehicles. 

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Grant  2022 GMC Denali 2500 HD 2019  Elite 11😎

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2 minutes ago, Landrover said:

Not sure about all the tech conversations. Never had a problem with the DEF fluid. My new GMC has a level gauge full to empty instead of a percentage of use, which makes it much easier to know when to add fluid. Adding fluid is usually 3-5000 miles of use, or every oil change. My mileage has increased to 16-18mpg  towing the Oliver. only have  3,000 miles on the truck. I expect this average to go higher once the engine breaks in. There also has been  a big increase in tow capacity 18,000 vs 13,500 on my 2017 HD diesel I thought my 2017 highcountry Duramax was over kill. 🤯 The comfort and safety level of the GMC with the diesel is worth putting in DEF fluid not happy about the fuel prices, who is? Still couldn’t be more happier with the choice of a diesel tow vehicle. 😎 you could also import this to Trainman’s post on tow vehicles. 

Forgot to add Def fluid  is available just about everywhere  fuel stations Walmart hardware stores. Until they have a shortage which is becoming the norm among items. 😡

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Grant  2022 GMC Denali 2500 HD 2019  Elite 11😎

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On 6/25/2022 at 12:23 PM, John E Davies said:

Since the DEF consumption rate is proportional to fuel burned, if you are towing an Ollie and getting say 16 to 18 mpg, you will be burning, almost twice as much DEF. I would appreciate hearing fuel and DEF consumption numbers from owners here, towing and not towing.

And have you ever NOT been able to find some when you needed it? Ever had your engine go into limp mode? How did you deal,with that?

Thanks.

John Davies

Spokane WA

John, I have been watching as many videos on YouTube that I can find on the EcoDiesels, but none that I can find ever ran there EcoDiesel till the engine shut down because of DEF fluid running out. Something else I saw today was some stations have DEF on a pump setup for it and it pumps DEF just like the other fuels do, it even has the automatic shutoff. Pretty soon a fuel island will be 10 ft. long and have 7-8 fluid fillers and one for electrical charging.  

trainman

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Elite II, Twin Bed, Hull #489, 2019 RAM 1500, 5.7 Hemi, 4X4, Crew Cab, 5'7" bed, Towing Package, 3.92 Gears.

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  • 3 weeks later...

I have the GM 1/2 ton with 3.0L diesel.  It definitely uses a lot more DEF fluid when towing but I haven't attempted to measure it.  Would say that it's for sure at least double usage, but it hasn't been a problem.  If I'm on a longer trip and the DEF tank is not topped off then I put a 2.5 Gal container in the bed just as convenience.  I haven't had trouble finding it and have picked it up at Costco, Walmart, Lowes, etc.   It's a bit of an inconvenience compared to a gasser but I'll gladly deal with it to get 18 MPG towing my LEII and 30 MPG on the highway not towing -- plus the low end torque, much less power loss at altitude (compared to gas) and the automatic engine brake is great on mountain descents.

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2020 Elite II #627, 2021 Silverado 1500 3.0L Duramax, Colorado

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10 hours ago, tallmandan said:

I have the GM 1/2 ton with 3.0L diesel.  It definitely uses a lot more DEF fluid when towing but I haven't attempted to measure it.  Would say that it's for sure at least double usage, but it hasn't been a problem.  If I'm on a longer trip and the DEF tank is not topped off then I put a 2.5 Gal container in the bed just as convenience.  I haven't had trouble finding it and have picked it up at Costco, Walmart, Lowes, etc.   It's a bit of an inconvenience compared to a gasser but I'll gladly deal with it to get 18 MPG towing my LEII and 30 MPG on the highway not towing -- plus the low end torque, much less power loss at altitude (compared to gas) and the automatic engine brake is great on mountain descents.

I agree with you.

trainman

Elite II, Twin Bed, Hull #489, 2019 RAM 1500, 5.7 Hemi, 4X4, Crew Cab, 5'7" bed, Towing Package, 3.92 Gears.

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The 3.0 Duramax is a powerful and efficient motor but it has some pretty significant design faults that are enraging some owners, a redesign is coming that will hopefully fix them. I personally would not keep any modern diesel beyond the warranty period, and I would accept the idea that the entire cab (or body on an SUV) of your 3.0 truck might have to come off at a GM dealer to fix it. If it won’t start part way through your dream vacation, you might regret your purchase decision… especially if you are completely stranded in northern British Columbia with NO cell connectivity, no dealer within 300 miles and no way to get to your destination in Alaska or to return home. Think about that for a while 😳😳

https://pickuptrucktalk.com/2022/01/3-0l-duramax-diesel-long-crank-issues-continue-to-confound-dealers-frustrate-owners/

https://pickuptrucktalk.com/2022/04/replaced-already-new-gm-3-0l-duramax-diesel-lz0-coming/

OTH I do love how the turbo is mounted up top where it is super easy to service. Unlike the new Tundra/ Sequoia gas V6 and all V8 turbodiesels…

84B5E859-86E6-4EF9-8069-9EE0430DF80A.thumb.webp.93cd8e3741341b9f1fc8fb7c2e92d9d1.webp

John Davies

Spokane WA

  • Like 1

"Mouse":  2017 Legacy Elite II NARV (Not An RV) Two Beds, Hull Number 218, See my HOW TO threads: https://olivertraveltrailers.com/topic/john-e-davies-how-to-threads-and-tech-articles-links/

Tow Vehicle: 2013 Land Cruiser 200, 33" LT tires, airbags, Safari snorkel.

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On 7/18/2022 at 7:20 AM, John E Davies said:

The 3.0 Duramax is a powerful and efficient motor but it has some pretty significant design faults that are enraging some owners, a redesign is coming that will hopefully fix them. I personally would not keep any modern diesel beyond the warranty period, and I would accept the idea that the entire cab (or body on an SUV) of your 3.0 truck might have to come off at a GM dealer to fix it. If it won’t start part way through your dream vacation, you might regret your purchase decision… especially if you are completely stranded in northern British Columbia with NO cell connectivity, no dealer within 300 miles and no way to get to your destination in Alaska or to return home. Think about that for a while 😳😳

https://pickuptrucktalk.com/2022/01/3-0l-duramax-diesel-long-crank-issues-continue-to-confound-dealers-frustrate-owners/

https://pickuptrucktalk.com/2022/04/replaced-already-new-gm-3-0l-duramax-diesel-lz0-coming/

OTH I do love how the turbo is mounted up top where it is super easy to service. Unlike the new Tundra/ Sequoia gas V6 and all V8 turbodiesels…

84B5E859-86E6-4EF9-8069-9EE0430DF80A.thumb.webp.93cd8e3741341b9f1fc8fb7c2e92d9d1.webp

John Davies

Spokane WA

Thanks for sharing the links john.  I value your knowledge and experience as an engineer (which I am not) and I really appreciate all the contributions you make on this forum!  I'm simply sharing my experience - in which I have been very impressed.  I am also a member of the 3.0L Duramax facebook forum.  I don't really do social media but you can get a lot of info and guage the "pulse" from the groups function of Facebook  (including Oliver).  It's true that many owners have experienced the crank/no start problem.  It's also true that a great many of owners have not.  In a year and 7 months of ownership, I have never had it happen.  I don't know what the percentage of units sold have reported this issue but I'm going to guess it's a significant minority.  Also, if you read about the problem, it doesn't leave anybody stranded as the truck starts on the second try.  I haven't had a single problem with the truck.  Now, it's early at 18k miles - and I do wonder - because I come from a bias of extremely good reliability experience from my trust old 2007 Toyota Sequoia.  I strongly considered a Tundra (2020 or 2021 model at the time) becuase of the demonstrated reliability but they suck gas, a lot of gas, and the towing package and tech on the GM was way ahead.  The LM2 engine was built from the ground-up for light duty trucks in joint collaboration with Issuzu Heavy Industries.  My understanding is that Issuzu has an excellent reputation for durable small deisels in Europe and Asia.  I bought it because the technology and efficiency are remarkable. The author of the two articles you cited says so himself -  

quote - "the LM2 is inherently balanced and provides a very smooth and powerful driving experience. It is one of my top five favorite engines on the market."

As for why they are replacing it, I'm going to guess it has to do with it's size.  It doesn't fit into new vehicle models as the author states.  It requires significant height in the engine compartment at a time when manufacturers are designing vehicles with more and more emphasis on aerodynamics.  If you look at the Chevy Silverado /GMC Sierra, they have a very tall front hood and square profile.  The 3.0 deisel takes every inch of space and I think the Silverado even requries a different hood with slightly higher profile than the gas engine models.

I will report back if I have any problems with my truck as this form is a helpful resource for Oliver owners.  Right now, my experience (n of 1) is that a 3.0L deisel mated to the 10 speed transmission are excellent to pull an Oliver Elite II.  

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2020 Elite II #627, 2021 Silverado 1500 3.0L Duramax, Colorado

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