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Old 07-27-2010, 09:15 AM   #1
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Gas vs Diesel Mileage

This is maybe a can of worms BUT
in comperable size MH's how does the
MPG compare gas vs diesel
also in several mh's we are looking at
i find both the ford chassie w/v10
and a workhorse w/ 8.1 in the same
year / model coaches or similar
the diesel is not too common in the size
we are looking at but the chioce
of the ford or workhorse is just a matter
of lookin harder - what you think
we are looking at 33 - 34 foot itascas
at the persent - 2004 -5's

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Old 07-27-2010, 09:50 AM   #2
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Gas motors are often found in motorhomes up to approx 36 feet. Anything over say 30 feet for a gas is just too much for it. The unit will suffer on loads and climbing hills.

Larger requires something more powerful. Diesel engines cost more, hence the reason for gas until gas is no longer able to do the work. The Ford Triton V10 is the largest RV gas engine available today. Fuel mileage is improved with the diesel, but the diesel engine will cost more. For the same weight load, gas may get 5 MPG, Diesel 7-8 MPG (~30-50%) 30% more likely. Diesel engines outlast gas by 2 or 3 times longer. This is ONLY due to over-engineering of the diesel motors. Gas engines could last as long if the manufactures over built them as well.

Approx Comparrison prices
Ford 6.0L $10k
Cummins 8.3L ISC $15k
Cunmmins 8.9L ISL or CAT C9 $20k
Cost keeps going up.

If someone has the actual cost for various motors,... It would be nice to know
$20k for a C9 or 8.9 ISL seems a bit high. Maybe for a C13

Basically, you buy a heavy duty diesel for some improved fuel economy, power (duty rating) and longevity over gas engines. You would never see an RV gas engine pulling an 80,000 lb load.

Note, since diesels will initially cost more and cost more to maintain, the savings may not benefit over a gas. If the unit exceeds the gas engine's capability, diesel will be the only way you can go.

I find vehicle manufactures tend to put only the size engine needed for the application. They don't tend to do an over-kill power unit since an over-kill results in an increase in purchase price $$$. Hence, the power unit I have could really use a step up or two.

Fleetwood Providence 2008 40e
Ford F-350 4x4 Diesel 6.0L 2006
Honda CR-V 2006
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Old 07-27-2010, 11:21 AM   #3
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Our 37' National with a 300HP Cat gives us 10MPG at 60-63 MPH. Gas coaches in the 30+ foot category will be lucky to see 7. Larger gas coaches are out there, I just read a review on a Winnie Adventurer around 35ft or so, multiple slides and lots of extras. The problem was it had less than 900lbs CCC. I guess you'd have to go on a diet.
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Old 07-27-2010, 11:31 AM   #4
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Most of the claims of 10mpg for large diesel motorhomes is inflated. I travel with a friend that has a 39ft diesel with cat 350 and his gas mileage is about 6 to 7mpg. I have a 35 ft Allegro bay with two slides and the chevy 8.1 on a w22 workhorse chassis and it makes about 8 to 9 mpg. I don't agree with some people who claim if it is over 30 ft, it does not have enough power. We recently returned from a trip to Arkansas, and I had all the power I needed. We drove to the mountains with a toad and some of the grades were 8 and 9%. The 8.1 chev is far superior to the ford v10 with more power and better mileage. Chevy will tell you that the 8.1 will last 2 to 300k miles. How many people do you know will put that kind of mileage on a mh?
If I had to do it again, I would go with workhorse. Iwent from an older model diesel to this 06 gas and I don't regret it a bit. That jingling you hear is the extra moneyI have by buying a gas.
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Old 07-27-2010, 06:32 PM   #5
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My 8.1 with Banks Torque tubes out performed many a DP on hills and easily popped up from 60 mph to 75mph to pass or cruse all day at 75mph in a 35 foot Triple E Commander ( a heavy coach). My new Triple E Empress (40 feet) with a 400 hp Cummings is a good puller but won't "snap" from 60 - 75mph. It is pushing another 10,000Lbs but still gets the 8.5 mpg I was getting with the Workhorse.
The 8.1 was far superior to the V10 I had in my 30ft Bigfoot (6-7 mpg) with little extra power.
I feel that the best bang for the buck was the 8.1.
Hope that helps.
2007 Triple E - Empress Elite - Freightliner
WH 22 owner for 7 years
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Old 07-27-2010, 06:45 PM   #6
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I have a 41' motorhome weighing in at 31,000 towing a 3,600 pound toad. After the Cummins ISL engine broke in the fuel mileage went up and the last 20K miles it has averaged 9.3 mpg. I don't think there is any gasoline engine that will get better than 9.3 mpg shoving 34,600 pounds down the road.
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Old 07-27-2010, 07:04 PM   #7
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"Gas motors are often found in motorhomes up to approx 36 feet. Anything over say 30 feet for a gas is just too much for it. The unit will suffer on loads and climbing hills"

Don't want our 37'8" coach reading this cause it doesn't know any better.

Will admit though, it sometimes struggles on hills a bit but always makes it over them.
Jim & SherrySeward

2000 Residency 3790 v10 w/tags 5 Star tune & Banks system Suzuki XL7 toad
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Old 07-27-2010, 07:07 PM   #8
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I can't compare Diesel vs Gas but can say on my recent 5500 mile trip that included Hwy 50, Vail pass, Raton pass, Jacob Lake, Kingsbury grade and a 20-30 MPH sidewind for 2 days in NV and TX, I averaged 7.6MPG while towing a Saturn Vue at 65MPH Max. I did have to endure a lot of front engine/fan noise while the fan clutch was engaged.

I don't travel enough to justify spending the extra for a diesel.
2003 Allegro, 32BA, W20,'06 Saturn Vue, Demco Aluminator, RM9700, R1150RT B'mer
SE Louisiana
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Old 07-27-2010, 08:13 PM   #9
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The Ford (or Workhorse) gas powertrains are great value for the money. Both will last at least 100K and even 200-300K with proper maintenance. The Ford powertrain in our 34' 2 slide coach has plenty of power, even on the 8% grades in the NC mountains it will keep up with and outrun trucks.

Having said that I'd love to have the money for a diesel coach, but our budget would not stand for it.

The number I've heard of most when comparing mileage for similar gas and diesel coaches is 20%, i.e. the gas coach gets 8MPG, the diesel gets almost 10. However, as you have found, diesel coaches in your year and size range are not that common.

One thing to watch our for is CCC, as other posters have mentioned some gas coaches (and some diesels too) have very low CCC's. Usually the more slides you have for a given rating chassis the lower the CCC is. For example, our coach has 2000lb CCC. A similar coach with 3 slides had only 1500LB CCC. So that extra slide cost you 500lb of CCC. This is the reason why some people choose diesel, because a mfr would take that same 3 slide design, put it on a diesel chassis, and have 4000lb CCC. At a price, of course.
Stewart, Brenda and kids
2008 Newmar Canyon Star 3410
2006 Roadtrek Versatile 210
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Old 07-27-2010, 08:51 PM   #10
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We just finished a 6000 mile trip from Texas to San Diego, up US-101 to Whidbey, Island, then headed acroos Idaho, Montana, Wyoming, Colorado, Oklahoma, and back home. Except for the very last 250 miles of my trip I averaged 9.6 mpg in my 40' MH with a Cummins ISB 6.7L, 340 hp engine. The last 250 miles of my trip when I pulled into the driveway it was at 10.0 mpg exactly. I have just over 20,000 miles on the engine. I guess it just got broken in.

In September we head the other direction. I'm interested in seeing how it does on the Eastern Seaboard.

In my earlier days, pulling about 14,000 pounds with 1 tons, a Chevy 454(gas) got about 4 mpg, a 1987 ford diesel got about 6 mpg, and a 2005 F350 King Ranch. Crew Cab, Long Bed, 6.0 diesel. got right at 10 mpg, give or take a few 10ths.
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Old 07-27-2010, 09:58 PM   #11
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diesel is about 25% more efficient

Years ago Motor Trend printed in their magazine that diesel motors averaged about 25% more efficient than gas. They said it had to do with the compression of the motor wringing more energy out of each unit of fuel. My own personal experience is this. My 1975 GMC that weighed 12,000 lbs averaged about 7.5 - 8 mpg on gas. My 2002 38,000 lb Affinity + towed Saturn averages about 7.5-8 mpg on diesel. Both went right up hills with no problem and both have plenty of power, or at least as much as you need.

The really HUGE advantage that most diesels have over gas coaches is that the motor is in the rear most of the time. Rear motors make for a far nicer driving experience. I realize that there are a few gas rear motor coaches and some front diesels. But the most common is gas motor in front and diesel in rear.
Bob & Barbara
2002 Country Coach Affinity
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Old 07-28-2010, 06:52 AM   #12
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THANKS for all the good information here
we are staying in the 33 34 foot range for the coach and we will buy a low mileage coach - most are gas.

Driving cost with all considered??
Driving 10,000 miles
gas coach @ 7mpg = 1400 gals @ lets say $ 2.65 = $3710.00
diesel Coach @ 10mpg = 1000 gals @ " " $ 2.95 = $2950.00
that’s a savings of $ 760.00 in 10,000 miles
If I have to pay $10,000 extra to get the diesel engine its going to take a while to recover just the cost of the diesel BUT the added CCC of the diesel could help along with the toad maybe - In the coaches we have looked at - We really like the Itasca's in the 32 -34 foot range. Have not seen a diesel in these - we see lots in the $45 to 55K (asking) range- this is 2004 - 05 models with low miles. we have NO plans for extended or full time use - 2-3 week to maybe a month at most. what we do find is the workhorse chevy chassis and the for V10 in the same units looks like the workhorse chevy set up is
a heavier more powerful chassis with more weight capacity
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Old 07-28-2010, 07:07 AM   #13
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Depends on the chassis the MH builder selected to put under the coach. A Ford 26k chassis with a 22k coach on it will have considerably more CCC than the same coach on a 24k Workhorse.

In the MH up to about 26k lbs, the cost numbers will go to the gas chassis every time. Diesel will never recoupe the cost. Over 26klbs diesel is the only option. There are lots of motorhomes up to 38ft that are well under that weight limit with plenty of CCC on a gas chassis. Just need to look. Most motorhomes ordered by dealers will take the standard chassis offering by the coach builder. Will be just enough for the weight of the coach plus a small CCC. Motorhomes ordered by clients will often order the upgraded chassis for the upcharge. IE the same model coach can be found on more than one chassis.

Our Damon would have come standard on a Ford 20.5k or Workhorse 20k chassis. The original owner bought the Ford 22k as an upgrade (likely forced at the time as the 242" chassis was not available yet in 20.5k when my coach was built) Anyway there are same model coaches as mine running around with much less CCC. (we have over 3000lbs CCC) You need to look.
38ft 2008 Damon Daybreak 3575 (forward kitchen)on Ford 22,000lb chasis, 242" WB.
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Old 07-28-2010, 08:26 AM   #14
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If you plan your budget based on 10 MPG in either gas or diesel you'll be disappointed. I'd plan on more between 6.5 and 8.5 MPG if you average over 10-15 tanks of fuel.

The single biggest factor is the weight of your right foot. That's about all YOU have control over. Winds, tail or head, up or down hill, city, country, freeway, 2-lane help or hinder mileage BUT you are the single biggest factor.

As mentioned, the CCC on some rigs is skimpy. Be sure to check that. Winnie/Itasca does or did make a 34 foot diesel.

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