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Old 05-22-2022, 03:06 PM   #1
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DEF usage

So my curiosity is up, I purchased a 2015 Newmar Essex with a Cummins ISX600 in March of 2020 with around 22,000 miles on it. So for it runs and drives fine, Iíve fixed a number of minor issues. My question is how much DEF are these supposed to use. I run the speed limit most of the time so 70-75 MPH for reference. The Coach gets around 4.9 MPG per the dash readout. In the past 5-1500 mile trips it appears to me my coach uses an extreme amount of DEF. I didnít track it to close until the most recent trips and I go through about 5-2.5 gallon containers of DEF each 1500 mile trip.
How much are you all using?

Not sure if this is normal or possibly I have an issue with my engine emissions system.
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Old 05-22-2022, 03:14 PM   #2
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On a 1,500 trip we use about 3 jugs but I drive at 65 and our MPG is 8.1 on the dash. We have a 450 HP, 9 liter, so to me, you look about right with the BIG Boy engine.
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Old 05-22-2022, 03:15 PM   #3
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Here is an old thread on this topic.
https://www.irv2.com/forums/f258/diesel-exhaust-fluid-update-495568.html
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Old 05-22-2022, 03:17 PM   #4
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You're pretty close to average. DEF runs about 3% - 5% of the fuel you use. In your case, you used right around 300 gallons of fuel in 1500 miles. You should have used between 9 - 15 gallons of DEF. You said you used 12.5 gallons, which is almost in the middle at 4%.

I don't track my usage as I just don't care. For rough estimates, I figure it at 3%. I like to keep my DEF tank full. After every 90-100 gallons I know I can put another 2.5 gallon jug in.
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Old 05-22-2022, 10:43 PM   #5
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Thanks for the quick reply feedback guys. DRM901, thanks for the thread reference. Don I normally am like you I don’t pay a lot of attention to how much fuel or in the case of DEF we use on a trip but thIs is my first Coach running DEF and it seemed extensive and just wanted to make sure I am in the normal range and not having a problem cropping up. This will help me rest a little easier know it’s is in the normal range.

Again to all thanks for the quick feedback.
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Old 05-23-2022, 07:03 AM   #6
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At first your usage based on miles seemed high to me, but I believe the math re def versus fuel usage. But your MPG seemed really low to me. On both of my bigger rigs ihave gotten 8-9 mpg(sometimes more), which translated into less def usage per mile Ö. But then again I consistently drive 65 mph. Of course, driving speed is an individual choice, but if you are worried about usage, it might be interesting to see what happens if you reduce speed for a while?
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Old 05-23-2022, 07:19 AM   #7
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That is typical usage for the 600 Cummins before mid 2018. My son's Newell has the pre 18 605 Cummins and he needs to add DEF at each fuel fill as it wouldn't make it to the next fill up. He also runs 70 and gets about 5 mpg. He has told me that the later engines use much less DEF due to a more efficient design. His build was 3 months before Newell went to the newer design. My little 450 Cummins uses a gallon of DEF about every 400 miles driving 62 mph and gets a little over 7 mpg towing a 6300# toad.
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Old 05-23-2022, 10:51 AM   #8
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When we got our 2018, we attended a Camp Freightliner seminar. We were told normal usage was about 1 gallon of def for 50 gallons of fuel. Which is about what we have been getting, 1 gallon of def per 390 miles, 7.75 mpg average.
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Old 05-23-2022, 11:58 AM   #9
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Quote:
Originally Posted by paddler1954 View Post
...We were told normal usage was about 1 gallon of def for 50 gallons of fuel...
Same here. DEF usage is based on gallons of fuel used.
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Old 05-23-2022, 04:12 PM   #10
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I get a thousand miles per jug. Slow down. More speed, more fuel and def. I get 8.8 mpg.
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Old 05-23-2022, 10:50 PM   #11
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Quote:
Originally Posted by MN_Traveler View Post
At first your usage based on miles seemed high to me, but I believe the math re def versus fuel usage. But your MPG seemed really low to me. On both of my bigger rigs ihave gotten 8-9 mpg(sometimes more), which translated into less def usage per mile Ö. But then again I consistently drive 65 mph. Of course, driving speed is an individual choice, but if you are worried about usage, it might be interesting to see what happens if you reduce speed for a while?
Itís not that I am particularly worried about the usage other than I wanted to know if my DEF usage is normal for my engine size and fuel usage.
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Old 05-23-2022, 10:51 PM   #12
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Quote:
Originally Posted by paddler1954 View Post
When we got our 2018, we attended a Camp Freightliner seminar. We were told normal usage was about 1 gallon of def for 50 gallons of fuel. Which is about what we have been getting, 1 gallon of def per 390 miles, 7.75 mpg average.
Based on what you were quoted by Freightliner it seems that my usage is normal based on my fuel used. Thanks
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Old 05-23-2022, 11:03 PM   #13
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Quote:
Originally Posted by Fiesta48 View Post
I get a thousand miles per jug. Slow down. More speed, more fuel and def. I get 8.8 mpg.
I donít think I could ever get that kind of fuel mileage out of my rig even at 60MPH. I also pull a loaded 24í trailer with a combined weight of approximately 64,000 pounds.
That said I do agree slower to a point typically will result in better fuel mileage. I just donít have the patience to drive 60-65 and donít mind paying the price for more fuel. I have a hard time running speed limit when it slows to 70MPH but try to abide by the law. I donít have to be the fastest guy on the road but I also donít want to hold up traffic. I also donít expect others to drive faster if they are not comfortable with it or choose not to, that is there privilege provided they arenít obstructing traffic or creating a hazard for other motorists.
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Old 05-23-2022, 11:15 PM   #14
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Thanks all for your response, my main concern for the post was to determine if I possibly have an issue with my engine or emissions system. From all of your responses it sounds as my use is normal for my circumstances and driving habits. I could possibly lighten up on the accelerator pedal and gain a MPG maybe plus or minus which should in theory cut my DEF usage. Sometime when I’m not on a schedule I will try to drive a tank of fuel at 65 and see what the plus or minuses are. That won’t be for a while. Probably won’t go on any long trips before January. Will see, thanks again.
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