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Here's an example of how DEF useage is tied to fuel useage.
Pulling my boat 460 miles round trip, 10.9mpg.
Just under half a tank of DEF left and only 498 miles estimated DEF range.
By the end of the week it will be back to normal but once its under 500 miles it won't reset until you add DEF. After adding 2.5 gallons it still only estimated 1100 mile range but should show around 4500 after a few days of non-towing.
 

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I have 2018 3.0 Question about Def usage.. Last oil change with 9,000 miles only use 3.0 gallons of def. Not any trailer pulling probably 50/50 HWY and town driving. Just seem low??
 

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@roundman2 - I have been tracking ~2.5 galons of DEF per 5K miles w/o towing for predominantly city driving, so your usage does seem on the low side.:
  • I have mine refilled as part of my Extended Maintenance plan every 5K miles with my oil change
  • I would ask your Service Writer/Manager if there is any way they can check if DEF system is operating normally...
 

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I have 2018 3.0 Question about Def usage.. Last oil change with 9,000 miles only use 3.0 gallons of def. Not any trailer pulling probably 50/50 HWY and town driving. Just seem low??
Here's an example of how DEF useage is tied to fuel useage.
Pulling my boat 460 miles round trip, 10.9mpg.
Just under half a tank of DEF left and only 498 miles estimated DEF range.
By the end of the week it will be back to normal but once its under 500 miles it won't reset until you add DEF. After adding 2.5 gallons it still only estimated 1100 mile range but should show around 4500 after a few days of non-towing.
DEF useage has nothing to do with fuel consumption, and everything to do with EGTs. The higher the temperatures, the more DEF it uses to counteract NOx formation. NOx is created through high combustion temps; it's the spontaneous combination of nitrogen and oxygen in the air at high temp. So if you tow more, you have higher EGTs, your exhaust sensor says "whoa thats a lot of NOx", and pumps in more DEF. If you don't tow and are just cruising around, your EGTs are lower, then EGR is enough to reduce the cylinder temps, and you don't need as much DEF.
 
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