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03-19-2005, 04:31 PM
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#1
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Senior Member
Newmar Owners Club
Join Date: Mar 2005
Location: Abbotsford, BC
Posts: 532
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Can anyone out there with a 400hp Cummins (preferably on a 43' MH) provide information on your average fuel economy?
We're stepping up from a 300hp 40' MH (which gets around 9 mpg)to a 400hp (Cummins ISL) 43' Mountain Aire... and with fuel prices rising so rapidly, we'd like to have an idea of what we might be getting ourselves into. 
Thanks!
- John
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John
2005 Newmar MADP
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03-19-2005, 04:31 PM
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#2
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Senior Member
Newmar Owners Club
Join Date: Mar 2005
Location: Abbotsford, BC
Posts: 532
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Can anyone out there with a 400hp Cummins (preferably on a 43' MH) provide information on your average fuel economy?
We're stepping up from a 300hp 40' MH (which gets around 9 mpg)to a 400hp (Cummins ISL) 43' Mountain Aire... and with fuel prices rising so rapidly, we'd like to have an idea of what we might be getting ourselves into.
Thanks!
- John
__________________
John
2005 Newmar MADP
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03-19-2005, 07:10 PM
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#3
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Guest
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....12 in my Volvo tractor loaded to 30,000#...t hen again I'm not a square brick....areo truck and v nose trailer....geof kaye
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03-20-2005, 12:22 AM
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#4
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Senior Member
Join Date: Feb 2000
Location: Erie, PA
Posts: 1,070
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 John & Peter, I would say not to except any more than 6-7 maybe 8 mpg according to what other owners have said. Ed. S
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2005 Newmar Mountain Aire W-24 , 2006 Jeep Commander Limited towed vehicle Newmar Kountry Klub 7284L, Pennsylvania State Directors
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03-20-2005, 03:44 AM
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#5
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Member
Join Date: May 2003
Location: Virginia
Posts: 41
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Towing our GMC Yukon XL toad we get about 8 - 8.5. Remember a diesel will have a sweet spot at around 2000 - 2200 RPM that will be the best mileage, then if you go above that spot by a mere 100 RPM you can loose 2 MPG.
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2004 Itasca Horizon 40KD, Cummins 8.9 ISL
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03-20-2005, 05:18 AM
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#6
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Senior Member
Newmar Owners Club
Join Date: Mar 2005
Location: Abbotsford, BC
Posts: 532
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Thanks, all.
Guess we'll just have to wait and see!
Foz: we'll definitely look at performance in that 2000-2200 rpm sweet spot.
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John
2005 Newmar MADP
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03-29-2005, 08:05 PM
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#7
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Junior Member
Join Date: Sep 2000
Location: Was Naples FL. Now Tamassee SC
Posts: 4
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What speed are you going at the 2000 to 2200 sweet spot? My 02 40' Allegro Bus with a 350 Cummins is turning 1840 at 70 MPH. It does 68 MPH in 5th gear at 2150. I think I would have to break most speed limits to reach the sweet spot in 6th.
Later ...Harry...
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03-29-2005, 08:27 PM
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#8
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Senior Member
Alpine Owners Club
Join Date: Jun 2004
Posts: 2,554
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I thought  the RPM that the engine makes the most torque would produce the best mileage. My ISC makes the most torque from 1300 to 1600 and according to my VMSpc that seems to be where I get the best mileage. 2000 RPM is pushing the big barn door pretty close to 80 mph  , and at that speed I'm sure my mileage will not be good.
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 Tom, Patty, Hannah "The Big Dog" and Abby Kat, Indianapolis, Indiana 2000 Alpine 36' FDS 72232, 2005 Blue Bird M450 LXI Our Photos
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03-30-2005, 03:49 AM
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#9
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Moderator Emeritus
Join Date: Oct 2002
Location: Sheboygan, WI
Posts: 5,642
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The biggest factor is the wind resistance, which increases exponentially as the speed increases. There's a big difference between driving at 60 versus 70. Unfortunately, I didn't by a coach with a Cummins 400 to drive at 60 so I pay at the pumps.  
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Mark & Leann Quasius
2016 Cornerstone 45A
2020 Jeep Gladiator Rubicon
2021 Jeep Wrangler Rubicon
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04-05-2005, 11:48 AM
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#10
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Senior Member
Entegra Owners Club
Join Date: Sep 2002
Posts: 276
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With 5,000 miles on mine, my overall average is 7.4 mpg. Most of my driving is interstate and I'm usually cruising around 60-65...
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Ron - 20o5 Prevost Marathon H3-45, 2021 Rubicon, 2017 Ram Ecodiesel
Riverbend Motorcoach Resort, Labelle, FL
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04-05-2005, 11:50 AM
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#11
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Senior Member
Entegra Owners Club
Join Date: Sep 2002
Posts: 276
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Opps, I forgot to upgrade my profile... 2005 Allegro Bus with Cummins 400
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Ron - 20o5 Prevost Marathon H3-45, 2021 Rubicon, 2017 Ram Ecodiesel
Riverbend Motorcoach Resort, Labelle, FL
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04-05-2005, 04:46 PM
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#12
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Member
Join Date: Apr 2000
Posts: 71
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I had a B series 24 valve that had a sweet spot ( more power better fuel mileage )according to Cummings at 2,400-2,700. This was a 24 valve engine. THe engine manufacturer can give you the skinny on hte sweet spot. My current 12 litre 400 likes to run at 1,400-1,600 this is between 55 and 70 mph
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1968 graduate of Southeast Asia School of Warfare
Duc Pho Campus Vietnam
2002 Winnebago Chieftain 39T W 22
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