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8.5 hauling a 40' trailer with 2 cars and loads of heavy tools in it. Averaging about 65-70 MPH. Really seemed to suck up the DEF with the big load on it.


Greg
DEF usage is a ratio to fuel usage.

Use more fuel, it will use more def

Should be somewhere close to 1.5 gallons on DEF per 100 gallons of fuel.
 

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This is what my 2018 CCLB has been doing. I have almost 18,000 miles on it since last July and overall hand calculated average is 16.53 mpg over the first 12,500 miles. The trucks on screen mpg shows around the same mpg as well with the best 50 miles at 25.1 mpg and best 400 at 20.7 mpg not towing either time. I run mine around 50 miles one way to work each day going around 65 mph and towing on weekends.
 

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DEF usage is a ratio to fuel usage.

Use more fuel, it will use more def

Should be somewhere close to 1.5 gallons on DEF per 100 gallons of fuel.

Don't mean to doubt this but are you sure that is how its metered? I put in one of those blue DEF boxes and it seemed to be gone in two tankfuls at my towing consumption (8.5 MPG)

Greg
 

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Pulled the boat 400 miles round trip 65mph to 75mph and got 11.7. This is with a 18ft. boat. Scares me about thinking what I will get with the 35ft 5th wheel. I now have 2500 miles on the truck. Just doesn't seem right after pulling with my 2015!
 

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Def consumption is a % of fuel used. If you use 100 gallons of fuel, you will use 1-1.5 gallons of def. So when towing, with lower miles per gallon, will yield more def use per mile.
 

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Def consumption is a % of fuel used. If you use 100 gallons of fuel, you will use 1-1.5 gallons of def. So when towing, with lower miles per gallon, will yield more def use per mile.
From what I hear the L5P uses more DEF than that. They use quite a bit more than the LML.
 

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From what I hear the L5P uses more DEF than that. They use quite a bit more than the LML.
My truck would indicated the 'quite a bit more' is a rumor started by those not correctly measuring consumption. (and those just wanting to hate on DEF)

Probably in part to the continuation of dealers not filling at delivery, complicated by adding to the tank, but not completely filling (so no way to know if it was filled to the same point as last time def was added).

Like the LML, the level 'indicator' isn't accurate enough for determining DEF mileage.



No doubt there will be some that have something wrong with them and will use an unusual amount -- just like happened with some of the LML's.


I guess this is a pointless discussion, unless we are provided with some sort of definition of 'quite a bit more'.
 

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350 Miles @ 70 to 75 mph pulling my RV trailer into a 40 mph head wind with rain and snow.
9.4 miles per gallon. (2018 GMC 3500HD)
 

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Average DEF usage is around 900 miles/gallon
Average distance between regens is around 830 miles
Average hwy fuel economy is 19.5-20 mpg
Lifetime fuel economy is 18.4 (about 80% hwy and/or rural roads; towing probably <10% of the time)
Best fuel economy (whole tank) is 20.4 mpg
All fuel economy numbers are hand calculated
49k on the odo
 

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Just got back from our semi-annual trip to Florida. 2018 GMC 3500 Duramax SRW with 16,000 miles on it. Left for Orlando from Burlington, Ontario Canada. Drove 1305 miles without towing; averaged 70 mph; got 20.8 mpg.
Towed 16,000 lb 44ft 5th wheel back home, total towing 1,250 miles (stopped in Niagara Falls Ontario); got 10.5 mpg towing.
I am really pleased with the 2018. The additional horse power and torque was really noticeable compared to my 2011 2500 HD Duramax. It did not gear down on most uphill climbs as the 2011 did. The best mileage I got on the 2011 was 11.1 mpg towing 14,000 40 ft 5th wheel, low was 9.9 mpg with headwind.
 

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New best of 20.5
 

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Update:
Best of 21.5 so far. Averaged 20.06 for June and 20.68 for July. Not too bad!
 

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Almost 65k on the truck and a lifetime average of 18.8 mpg. I have gone over 700 miles on a tank a couple of times. I get around 14 mpg pulling my 3-horse slant aluminum horse trailer with small living quarters.
 

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Did a 3000 loop, illinois to co, wy,into sd. Big grades, got 11.7, that was calculated by hand, waiting for the 21's . There is noise within gm of big things on horizon. Good friend of mine is in the upper eschalon at gmc, I'll let all know what uncle chuck can find out,,, see ya WT
 

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Savannah to Balsam, NC. 700 miles RT. Lots of IH95 and IH26 at 80 and stretches at 90 (when IH95 is running fast, it runs fast). Mountains (hills) on IH26 South of Asheville. Overall DIC was 18.3. For an aerodynamic brick at those speeds, I think that's pretty impressive.
 

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Just got back from our semi-annual trip to Florida. 2018 GMC 3500 Duramax SRW with 16,000 miles on it. Left for Orlando from Burlington, Ontario Canada. Drove 1305 miles without towing; averaged 70 mph; got 20.8 mpg.
Towed 16,000 lb 44ft 5th wheel back home, total towing 1,250 miles (stopped in Niagara Falls Ontario); got 10.5 mpg towing.
I am really pleased with the 2018. The additional horse power and torque was really noticeable compared to my 2011 2500 HD Duramax. It did not gear down on most uphill climbs as the 2011 did. The best mileage I got on the 2011 was 11.1 mpg towing 14,000 40 ft 5th wheel, low was 9.9 mpg with headwind.
just did the near identical trip - niagara on the lake to fort wilderness campground with a stop in knoxville. so a bit of the smokies.

got 11.5 MPG in the mountains - never checked the overall mileage on the trip meter yet.
 

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Just finished towing 2200 miles to North East Saskatchewan and back towing an 18 ft fishing boat and averaged right at 15 mpg. Deringer in level 6 the whole way, 3 regens and 2.5 gallons of Def fluid.
 
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