RamRider

Central Texas

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I usually top up my DEF at around 6000 miles or when it shows 1/2 full. Use of DEF is proportional to fuel use, thus when towing you will use more fuel and more DEF but even so you are not using much DEF
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ShinerBock

LVTX

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The DEF usage ratio is about 50 to 1 per Cummins meaning for every 50 gallons of diesel fuel burned, you will use 1 gallon of DEF. The less miles per gallon you get in fuel, the less miles per gallon you get in DEF. So if you are getting 15 mpg, then you are getting 750 mpg in DEF. If you are getting 10 mpg, then you are getting 500 mpg in DEF. Basically, multiply 50 times your MPG and you will get your DEF mpg.
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ACZL

UPstate,NY

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As already stated, it varies a lot (towing VS not towing), but in general, you will only fill the DEF 1-2x/yr.
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markandkim

Swansea, MA.

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Bionic Man wrote: In theory, you should need DEF about the same time you need an oil change. But there are a LOT of variables to that.
Your DEF gauge is probably working just fine. You shouldn't need to fill after 6 tanks of fuel. According to Cummins, DEF consumption is 3% - 5% of your total fuel consumption.
The DEF tank on a 2016 2500 is 5.5 gallons.
It won't last 15000 miles. That is when the oil change is due.
1/2 of a tank of DEF goes about 3000 miles.
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mudfuel07

North Florida!

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When I had to use it on mine, I think I was putting in a jug every couple of months, maybe every 5-6 tanks. It really burns through it when towing, I felt like I could see the gauge move.
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trail-explorer

NM

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samhain7 wrote: Hi all
I am on tank of gas # 6 on my new to me truck and thrnDEF fluid gage has barely even moved
Why does a gas powered truck have a DEF gauge?
Bob
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wanderingbob

monticeeo, fla

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On my 2500 CTD , when gauge sez 1/2 I pour in 2 1/2 gallons . But you are correct , it will say full and then " bang " , it is on half !
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BurbMan

Indianapolis, IN

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My DEF gauge sat at F all summer, then we took 1000 mile road trip to PA with the camper and I used 1/2 tank of DEF. This is my first diesel truck and one thing I found out is that DEF has an expiration date, and stale DEF can clog up expensive parts.
I took the camper out one more time and DEF is at 3/8...but camper is winterized and it might stay at 3/8 till next year, so I'm not in a hurry to go out and buy more just yet.
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Learjet

Louisiana

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this video will answer and show you how the DEF gauge works
https://youtu.be/czJZuc8ThhI
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samhain7

Toronto

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Lynnmor wrote: samhain7 wrote: Lynnmor wrote: Your gas truck will run forever without filling the DEF tank.
The answer to your question is in the owners manual.
Gee, thanks for the help
![rolleyes [emoticon]](https://forums.goodsamclub.com/sharedcontent/cfb/images/rolleyes.gif)
You're welcome.
I just thought that I didn't want to sit and type up everything that you already have in your possession. ![rolleyes [emoticon]](https://forums.goodsamclub.com/sharedcontent/cfb/images/rolleyes.gif)
Then don't answer. Like at all
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