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Old 07-06-2022, 10:18 PM   #1
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DEF and a New to me TV

So my new to me TV (1st diesel), the DEF gauge reads 3/8 of a tank. I'm try to determine when I should add more.

The dealer had the truck 6 months before I bought it. It was a fleet lease return. Who knows how old the DEF is in the tank. So far I have used a bit over 1/8 of a tank, in 850 miles since purchased. FYI, this is an awesome tow rig.

What's your thoughts on when to add more DEF? I'm thinking when I get down to a 1/4 tank. Then I was thinking only adding a 2.5 gallon jug. Dilute and burn down, and then fill as needed.

Would I be better off waiting until an 1/8 tank? Or am I better off to top off the tank? Per the owner's manual it reads full around 5 or 5.5 gallons, but it is a 7 gallon tank.

Thanks
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Old 07-06-2022, 10:31 PM   #2
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Hey J and congrats on the truck. I have a 2019 and yes they are tow beasts. I wouldn't run it down too low as it will go into a limp mode. When mine gets to 1/2 on the DEF meter I can add 2.5 gal jug and it takes it to full. I try to never let it go below half if I can and carry a 2.5 gal jug when traveling just in case but do use the def pump at the truck stops. I don't use much when not towing but do go thru quite a bit towing.
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Old 07-07-2022, 02:02 AM   #3
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1/2 mark you can safely add 2.5 gallons...

watch this video to learn how the gauge works....

https://youtu.be/czJZuc8ThhI
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Old 07-07-2022, 04:06 AM   #4
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DEF is generally good for 2 years after manufacture, but high temps degrade it. IF you are concerned, Get a refractometer for checking DEF, around $20 on Amazon. Bought my D max new, had 1/2 tank of DEF, dealer said I'll make it to first oil change.. nope. Some local driving and hitching up the 5er for a 6 hr trip I got a low DEF warning. Towing will use more. IIRC, it's around a 50:1 ratio of fuel to DEF, so burn more fuel, use more DEF. I always carry a extra 2.5 gal jug in the 5er.
BTW, API and / or ISO 15022241 DEF meets all standards, no need to buy the expensive Blue DEF unless you don't mind burning extra cash. Check the jug seals in the store, there have been stories of returned DEF jugs filled with water.
I'll never tow heavy with a gas engine again, you'll like it!
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Old 07-07-2022, 08:01 AM   #5
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It’s a bit of “apples vs oranges” but my ‘13 F350 has a 5 gal DEF tank. The tank gauge isn’t very accurate and if I get a 2.5 gal jug and fill it when it says 1/2 empty I’ll have a quart or so too much. I’ve found I get around 1000 mi/gal of DEF.
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Old 07-07-2022, 09:39 AM   #6
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The issue to my knowledge with a refractometer. There is no method to pull a sample from the tank.

I know this truck came from Michigan, so it has not been sitting in year round sweltering heat.

Maybe I'll add a jug now.
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Old 07-07-2022, 10:28 AM   #7
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I have a 2017 f350 I refill at 1/2 tank and it will take a 2.5 gallon jug and brings it back to full.
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Old 07-07-2022, 01:22 PM   #8
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On my 2013 Touareg TDI the tank size is approximately 2.5 gallons and that lasts me 10,000 miles ( you read that correctly) 10k. I average 13,000 miles a year as you can see from my pic. of just a few minutes ago so it lasts about 9 months in my tank. It has never taken 2 gal. when I have to add it at 10.
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Old 07-07-2022, 01:59 PM   #9
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Quote:
Originally Posted by Jagiven View Post
The issue to my knowledge with a refractometer. There is no method to pull a sample from the tank.

I know this truck came from Michigan, so it has not been sitting in year round sweltering heat.

Maybe I'll add a jug now.
I have some of these to draw from the tank. Don't know if it will work with your truck with the DEF tank location, but they work well for the tank location under the hood of my Sprinter.

https://www.amazon.com/BIPEE-Graduat...ps%2C78&sr=8-6
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Old 07-09-2022, 04:46 PM   #10
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anyone find it interesting that DEF manufactures recently announced a shortage in supply chains, then they doubled the cost and we never saw the shortage as promised..Store shelfs are overfilled with the stuff.. This stuff is getting old...
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Old 07-09-2022, 07:51 PM   #11
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are you taking a trip soon? if not then the recommendation is to run it down as low as possible using up as much of the old DEF as possible.. generally i get down to around 10% give or take then fill it up at a def station. If you are traveling before you leave fill it up then keep 2.5 gal around in case you can't get it while traveling... your truck will eat it much faster with the trailer on it.. it is based on fuel usage. My experience has been when getting around 18mpg or so unloaded and 8mpg loaded i use it at about twice the rate.

YMMV but for me this has been pretty accurate for my 2019. Unloaded I get 5-6k miles loaded 3-4k miles per def fill.

You're lucky to have a gauge mine just says ok till it is down 30% and sometimes i get a surprise when it says 10% skipping the 30% warning...
Don't over think it.
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Old 07-10-2022, 04:34 AM   #12
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I have found that my '21 Ram with the Cummins engine loves the stuff!! Worse when towing. Previously I had a Ram 1500 with the Eco Diesel engine, and it used DEF very sparingly. I now refill around 1/2 tank, and it will take a 2.5-gallon jug.
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Old 07-10-2022, 05:17 AM   #13
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anyone find it interesting that DEF manufactures recently announced a shortage in supply chains, then they doubled the cost and we never saw the shortage as promised..Store shelfs are overfilled with the stuff.. This stuff is getting old...
They learned that trick from big oil and it works until the bottom falls out, then they undergo an overnight albeit temporary conversion to socialism ( when taxpayers bail them out) before reverting back to laissez faire capitalism.
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Old 07-11-2022, 07:45 PM   #14
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They learned that trick from big oil and it works until the bottom falls out, then they undergo an overnight albeit temporary conversion to socialism ( when taxpayers bail them out) before reverting back to laissez faire capitalism.
many of us knew that, But a small handful are blind.
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Old 07-13-2022, 09:24 PM   #15
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I asked my local mechanic about this very topic. He told me to treat DEF like milk, if it sits in the trucks tank too long it will go sour and cause issues with the injector and other components in the system. I usually only keep 1 or 2 boxes witting around my shop, but if I'm going on a trip, I'll get enough to last the entire trip. I have an 18 Ram 2500 4X4 and I use about a 2.5 gallon jug every 1500 miles or so towing my rig at 65. The manual for my truck says when the low-DEF light comes on, I can add 5 gallons. The tank capacity is supposed to be 5.5 gallons. However, I've stopped within a few miles of the light coming on to add DEF only to overflow the tank. I've also gone about 50 miles after the low-DEF light came on and STILL overflowed the tank. Now, I run it till the light comes on and add a single 2.5-gallon jug which usually brings the gauge to between half and 3/4. We have a 6500-mile trip planned; leaving in about 10 days and I have I think 6 boxes of DEF in the bed of the truck ready to go.
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Old 07-14-2022, 07:41 AM   #16
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Yup, as mentioned...I only go to half a tank then add 2.5 gls to full. I fill at pump at truck stops, super easy and way cheaper!!!

Happy trails!
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Old 07-14-2022, 10:53 AM   #17
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Jagiven,
I have a TV similar to yours (2021 3500 / HO Cummins, etc.) My learnings have been the following (which follows many of the others on the thread): Refill DEF when @ 1/2 if possible. It will be one 2.5 gal to fill. When on a road trip, I might push to 1/4 to time with fuel stop. If on road trip, try to fill fuel & DEF at the pump since the DEF is fresher there & no risk of tampering. When not on road trip, I just grab a 2.5 gal container when I reach the 1/2 full mark. Note that we use the truck primarily for towing & road trips, not much around town due to its size.
I take 1 - 2 DEF containers when on a long towing trip "just in case". This came true on part of my 7K trip last summer on sections away from the freeways ( i.e US 2 from Glacier to Minot). We ran into stations that had no DEF available & my "back-up" came into play. As I get near the end of my trip, I start to use up these "safety DEF containers" so they do not end up sitting in the garage for several months.
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Old 07-14-2022, 12:51 PM   #18
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My first diesel also. I have a F250 and when it gets 1/2 a tank the alarms start sounding off. I believe you go through it faster when towing.
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