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Old 06-05-2013, 07:17 AM   #1
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Fuel Economy ISB 5.9 vs ISB 6.7

Comparing the fuel economy of the newer 6.7 ISB to the older 5.9 ISB is tricky, but in the cases where there are similar weight vehicles with both engines what is the comparison? I know the 6.7 has more power but maybe it gained some efficiency to partially offset it.
Jim Walker
N Virginia
2014 Palazzo 33.2
Cummins 6.7 ISB, Allison 2100 6 Speed
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Old 06-05-2013, 07:25 AM   #2
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I have a 2013 SportsCoach 385DS (39.5 feet weighing 28k lbs) with the 6.7 ISB. We consistantly get 10.5 mpg (both on the trip computer and hand computed using mileage and full tank) travelling the east coast with or without the 3k lb Chevy Cruze Toad.

Not the fastest rig out there... but gets me there with decent mpg!

2013 Coachmen SportsCoach 385DS
2010 HD CVO StreetGlide
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Old 06-05-2013, 07:26 AM   #3
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The 6.7L was introduced to meet the much more stringent EPA emissions regulations that took effect on January 1, 2007. Therefore, it has more exhaust aftertreatment/regeneration equipment and requirements, more EGR, etc. than the 5.9L. Because of the tighter emissions requirements it must meet, fuel economy for the 6.7L tends to be slightly less than the 5.9L. Having said that, the 6.7Ls that utilize DEF will get about 10% better mileage (per Cummins) than those that don't (such as those utilized in the pre-2013 Ram pickups), but the cost of the DEF must be factored in.

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Old 06-05-2013, 10:50 AM   #4
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My guess with Mel's setup, either he is driving very hard or the brakes are dragging on his toad, everyone at the fuel pumps witth that setup all tell me they ar getting 12-14 mpg, Wonder what is wrong with Mel's set up ?
Dave M
Foretravel, 2001, 36' ISM500 "Hot Rod"
F150 w/EZ Golf Cart or
CanAM 800 Max Limited ATV
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Old 06-05-2013, 06:54 PM   #5
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Over ~51000 miles our 5.9l ISB has averaged 9.5 mpg. That's pulling a Saturn Vue and traveling from one coast to the other. through the Rockies, the plains, the eastern mountains, and the flat lands around the Gulf of Mexico.
Jim and Lynda, (Sophie, Jake, attack trained killer Shi-Tzus :-))

2003 Fleetwood Expedition 38N 2005 Saturn Vue
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