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02-01-2018, 04:47 AM
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#1
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Junior Member
Join Date: Jul 2017
Posts: 5
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Diesel Fuel economy
A dealer is telling me a 10 year old Cummins diesel in a 35 ft coach will get 15+ mpg. I am having a hard time believing this. What is the likely MPG at highway speed? Is there a brand, year, or configuration (other than the little MB diesel) that is remarkably better? THanks....I am new at this and my gut says diesel but gas is so much cheaper it makes it tough decision.
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02-01-2018, 05:01 AM
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#2
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Member
Join Date: May 2017
Location: Williamsburg, Ohio
Posts: 72
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My 16 year old 40’ 8.9 liter Cummins gets @ 8.3 mpg on the highway doing @ 65 mph. 15 sounds awful high
__________________
2002 MADP 4095
2016 Jeep Wrangler Unlimited
Dale
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02-01-2018, 05:05 AM
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#3
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Junior Member
Join Date: Apr 2012
Posts: 8
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I have owned several diesels, I think he diesel is a way nicer riding machine that I gas. I doubt you will see anything over 10 miles per gallon and you will be lucky to see 10 miles per gallon. And a gas machine pulling 35 foot of motorhome you'll probably see five or six miles per gallon.
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02-01-2018, 06:40 AM
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#4
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Moderator Emeritus
Monaco Owners Club Texas Boomers Club
Join Date: Nov 2015
Location: Central Texas
Posts: 13,426
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I get a consistent 7.5 mpg.
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Dennis and Katherine
2000 Monaco Dynasty
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02-01-2018, 07:01 AM
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#5
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Senior Member
Newmar Owners Club
Join Date: Jun 2012
Location: Spicewood Texas (West of Austin)
Posts: 4,514
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Quote:
Originally Posted by newbeeRV
A dealer is telling me a 10 year old Cummins diesel in a 35 ft coach will get 15+ mpg. I am having a hard time believing this. What is the likely MPG at highway speed? Is there a brand, year, or configuration (other than the little MB diesel) that is remarkably better? THanks....I am new at this and my gut says diesel but gas is so much cheaper it makes it tough decision.
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My F250 diesel pickup barely gets more than 15 MPG on the highway.
__________________
Scotty and Kristen, Airedales Dagny and Wyatt
2007 Newmar Mountain Aire 4528, 450 HP ISM, Allison 4000, 8 Lifeline AGM's
2019 F250 King Ranch 4x4 Powerstroke - SOLD
2022 F350 DRW King Ranch 4 x 4
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02-01-2018, 07:31 AM
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#6
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Senior Member
Join Date: Jun 2011
Location: FL
Posts: 11,440
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Someone is blowing smoke.
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Certified Senior Electronic Technician, Telecommunications Engineer, Telecommunications repair Service Center Owner, Original owner HR 2008
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02-01-2018, 07:40 AM
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#7
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Registered User
Join Date: Aug 2014
Location: western NC mountains!
Posts: 4,106
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I've seen an average of nearly as high from the N Georgia mountains to S Central Georgia... and I've seen averages much less in other areas of the country, depending on headwinds, weight on board, whether towing, etc.,,, but our average, over 80,000 miles of travels, no matter how often between resets, or how long between them, it always settle to 12.4mpg, or 11.4mpg with a tow vehicle.
-25,750lb freightliner XCS chassis/motorhome loaded
-2,800lb tow vehicle, tow bar, hitch extension
-Cummins isb6.7l 300hp with Allison 2100MH 6 speed transmission
these 'compact' diesels are the sweet spot in the industry, and this is a big reason why. I've delivered new units from the factories to dealers around the country, and the Thor Palazzo, Fleetwood Pace Arrow(formerly Excursion) and similar 34'-35' isb engine coaches average very similar numbers during deliveries.
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02-01-2018, 11:11 AM
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#8
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Registered User
Join Date: Feb 2008
Posts: 3,607
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Ask him where the patch of funny weed is that he has been grazing in. 8.0-8.5 would be a reasonable estimate. Better if you drive at 55 and worse if you put your foot in it. Plan for something reasonable and if you do better, be pleasantly surprised. We pull a full sized pickup, loaded to 8,500# when we go to Alaska and don't notice a significant difference loaded at that weight vs 4800 unloaded going up. We've driven up 7 times.
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02-01-2018, 05:03 PM
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#9
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Senior Member
Join Date: May 2017
Location: Metamora, MI
Posts: 5,525
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Seems like "all" DPs get 7 - 8.5 mpg No matter their load or destination, or pretty much the speed people say they drive.
Mine: 7.5 or so.
__________________
2002 Newmar Mountain Aire Limited 4370 w/ Spartan K2 and Cummins 500hp
ASE Master Certified (a long.....time ago...)
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02-01-2018, 05:34 PM
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#10
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Senior Member
Nor'easters Club Holiday Rambler Owners Club
Join Date: Oct 2016
Location: Monadnock Region of New Hampshire
Posts: 1,519
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Quote:
Originally Posted by Dav L
Seems like "all" DPs get 7 - 8.5 mpg No matter their load or destination, or pretty much the speed people say they drive.
Mine: 7.5 or so.
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Interesting, I get 7 to 8.5 most of the time as well. I have had worse (bad traffic for hours and hours dropped it down a lot due to stop-and-go...)
__________________
My name is Peter, and I'm never going to grow up.
- Winnebago Era 2010 Class B
- Holiday Rambler 2006 Ambassador 40-DFD Class A
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02-01-2018, 05:45 PM
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#11
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Senior Member
Official iRV2 Sponsor
Join Date: May 2011
Posts: 8,305
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Quote:
Originally Posted by Dav L
Seems like "all" DPs get 7 - 8.5 mpg No matter their load or destination, or pretty much the speed people say they drive.
Mine: 7.5 or so.
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I'll drink to that!
__________________
Joel (AKA docj)--
RV Technology Specialist
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02-01-2018, 08:06 PM
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#12
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Senior Member
Monaco Owners Club
Join Date: Mar 2012
Location: Angola State Prison - Murder
Posts: 4,230
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I hope this isn’t a double post. Our 07 Dynasty has averaged 7.5 mpg over 90,000 miles. It is a 44’ and very close to 50k lbs with the toad.
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John & Clare Lyon
2007 43.5' Monaco Dynasty Palace III (All Electric)
Towd: 2011 Chevy Equinox
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02-01-2018, 08:10 PM
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#13
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Senior Member
Join Date: Sep 2010
Posts: 4,515
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We are very pleased with our new 18 London Aire with Spartan K3 605 engine getting a solid 7 mpg at 65 and total weight of 55K. Had a Essex with a 500 ISM that was getting 6.5 at best and 7K pounds lighter. Should be able to get high 7 after 40K miles and slow down to 62 which is only 1300 RPM.
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02-01-2018, 08:11 PM
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#14
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Senior Member
Join Date: Aug 2017
Posts: 698
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Quote:
Originally Posted by newbeeRV
A dealer is telling me a 10 year old Cummins diesel in a 35 ft coach will get 15+ mpg. I am having a hard time believing this....
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As you should.
Your dealer is either a liar or clueless. There is NO WAY that coach will see double-digit MPG on a regular basis.
You will see 7.5 to 8 mpg, just like everyone else driving a diesel in a 35-foot coach.
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