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DEF Fluid Questions

2K views 18 replies 10 participants last post by  RED07LMM 
#1 ·
I am trying to do my learning on the fly with the DEF as well. Just had to take my truck back to dealer for DEF fill only after 900 miles. The service adviser said it probably wasn't filled when I bought the truck a few weeks ago. Took 4 gal after 900 miles of plain driving and no towing.

The dealer did not want to give me straight answer on how long a take will last due to different driving habits, environmental conditions, and towing. I am just trying to figure out how long a full tank of DEF will last with normal driving? If anyone can enlighten me, I would definitely appreciate it.

Josh
 
#2 ·
The longest I have gone on a tank of DEF in my 2012 is about 8000 miles. It's typically about 5000 miles. I'm anxious to see how long this latest tank is going to last since they just replaced the injector.

It may be very difficult to get a straight answer on this issue given the amount of problems these trucks have with the DEF system. It's a crying shame that a completely unnecessary system causes so many problems with reliability.
 
#3 ·
No kidding... If I get 5k miles out of a tank of DEF I will be happy. I just didn't want to add it every 1-2k miles. That makes it a PITA for long trips. Thanks for the info!!

Josh
 
#5 ·
Thanks Garrett!! This will help me determine if the DEF is being used at a normal rate or not. If it doesn't make it 5k under normal driving conditions I will be having the dealer investigate it. I am not saying it is an issue right now, but it definitely helps me gauge my usage.
 
#7 ·
Run it until it nags you for being low. Add 2) 2.5 gallon jugs (fresh sealed) pouring the last one slowly to avoid burps. I had great luck with Terra Caire DEF when I was running it. I have since set up so I do not need the DEF any more, but left the exhaust stock with DPF.
 
#16 ·
I just bought a 2015 Denali and was thinking this exact thing, about turning off the regen but keeping the stock exhaust until I can do a full delete. Is this basically what you did? Using EFI Live?
 
#8 ·
All def is manufactured to the same ISO standard.

Expect to use about 1.25 gal def for every 100 gal of diesel (ie 1.25%).

When the truck works harder and uses more fuel it will also use more def, in about the same ratio.
 
#10 ·
Speaking from experience, the better I made mine run (better MPG as well) more DEF it used to a point that it would be empty in about 2,000 miles. If we had the ability to control the amount used in the tuning I would gladly continue use, but since we can't I discontinued using it altogether. Truck just runs so much better when tuned properly.
 
#11 ·
Dealers definitely suck. I don't mind raising H&@/ at the dealer to get my way. Sucks it has to come to that but I will do it if need be.

I appreciate all the added info from everyone. I will use it to fuel my arguments with the dealer.

Thanks Again

Josh
 
#12 ·
How many miles on the truck? I wouldn't bother complaining until you had some real data. Odds are the dealer did not fill the tank so as I suggested add 5 gallons, log the mileage, and drive it. After you have several fills through it (say 20k on the clock) THEN you can start to get excited about how it is performing
 
#14 ·
Yes, I plan on collecting data before I begin to worry. I only have 1k miles on the truck! Most of my daily driving is rural roads at about 50-60mph and some city.

I didn't mean to sound like I was gonna fly off the handle for little or no reason. Just trying to learn about DEF usage so if there is a problem I'll have accurate data.

I appreciate the input y'all.

Josh
 
#15 ·
I have had a 2011, 2013, and now a 2015 Duramax. None of them have/had issues with the emissions system, but DEF consumption varies/varied widely because a number of normal driving factors affect the consumption, not just problems with components. Sometimes I have ploughed through DEF so fast I thought the injector line had a leak, and other times, like the past 3 months, the truck hardly seems to have used any.

The amount of DEF needed by the SCR depends on NOX levels in the exhaust, which are all over the map depending on engine load, and driving conditions, such as stop/start driving, steady state speed, rapid acceleration, and hilly or mountainous roads. The system compares the upstream and downstream NOX measurements and adjusts DEF injection so as to meet the required specifications. (There are generally different specifications for NOX while the engine is under load, as when hauling a heavy fifth wheel, or when the bed is full of cinder blocks).

DEF is also injected at the end of a regeneration cycle to help with the SCR/DPF cooling process, so more frequent regenerations will also increase DEF consumption. In other words, the amount of soot being produced will contribute indirectly to DEF consumption.

After carefully observing DEF consumption and regeneration behavior in my 2011, 2013, and 2015 I have come to the conclusion that there is no reliable guide to predict what you should expect between DEF top ups. Better to take a long range view, and measure consumption over several months. Then work out what you are using per thousand miles/kms and you'll have an average that might be more helpful than just taking "snapshots" along the way.
 
#17 ·
You can't simply "turn off the DEF". The NOX sensors in the exhaust system are there to ensure that NOX is within spec, and if there's no DEF to break down the NOX your truck will throw codes very quickly. Unfortunately, it is the type of situation that rapidly leads to speed limitation and eventually limp mode, around 4 mph.

Turning off the DEF supply would also require changes to the ECM programming so that the truck doesn't know that it has an SCR or NOX sensors, which is very difficult in 2015s. In fact, it is supposed to be impossible for 2015s.

On top of all that, your warranty is out the door if you interfere with the emissions system.

Why not just relax and enjoy your amazing truck as is.
 
#18 ·
I agree with keeping it stock especially on the '15's. But then again I'd never drive my LML stock again.

You cannot leave the filter in and stop regens. That would load the filter until it was plugged tight.
 
#19 · (Edited)
I don't mind keeping it stock for now, I just know how good my LMM ran after the delete. These trucks have so much potential but are very restricted coming from the factory, I keep telling myself that there is no reason to tear into my brand new truck, YET. That doesn't mean I can't learn all about it and get a game plan for when I do start to modify it.

Thanks for the input guys!
 
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