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Old 06-23-2013, 11:55 PM   #15
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Another factor that has hurt us over the years are the new, less efficient EPA mandated bio-diesel formulations. Cost goes up and our mileage goes down :(
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Old 06-24-2013, 12:42 AM   #16
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Quote:
Originally Posted by wimberleyman View Post
Anywhere between 8.3 and 10.5 pulling a toad. For me it all depends on the wind. More wind, worse mileage. Interesting thing is best mileage (10.5) was in the mountains but no wind. Go figure!

WM
Haven't read the Cat articles linked above, but like you, wind speed and direction seems to make the biggest impact on my fuel economy.

This would be consistent with an article I read in Car and Driver many, many years ago. In that article Car and Driver pointed out that when driving the average automobile at highway speeds, 85% of the energy exerted is just moving air out if the way. As the drag co-efficient of the average motorhome is about the same as a brick (much worse than the average automobile) I can only guess that the energy exerted is at least 85%.

BTW... I have a'93 HR Navigator, 38 DP, with a Cummins C8.3, and GVWR of 29k.

I attribute my fuel economy to an engine that just happens to be running at peak efficiency, and the fact that my motorhome has less air drag than most. It is a '93 model that's only 96 inches wide, it has basement air so no A/Cs on the roof. In fact, there is very little on the roof to disrupt airflow. No tall vent covers, no satellite dish, no air horns (they're behind the front bumper) and as mentioned, no air conditioners.

All if this helps it to slip through the air just a little easier than most.
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Old 06-24-2013, 01:04 AM   #17
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The Cat. information on RV . performance should be required reading for all diesel owners.
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Old 06-24-2013, 03:07 AM   #18
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We just completed a 7400 mile trip to the lower 48. Going down with a 2003 Endeavor with a 330 HP Cummins, pulling a 1999 Dodge Durango we got 8.3MPG. We picked up the 'new to us' 2009 Diplomat with a 400 HP Cummins, pulling the same vehicle and we put 68 hours of generator time, we got 7.7MPG. While I was a little disappointed in the MPG it is not bad considering the conditions we drove. Besides as it has already be said, it take fuel to feed those ponies.
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Old 06-24-2013, 05:35 AM   #19
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7.7 sounds good pulling a toad. I have a 2002 Newmar Dutchstar 3852 with a 330 cat and do not pull a toad and my silver leaf says my average over 72000 miles is 7.4mpg. I have put 12000 miles on in 11 months without a toad.
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Old 06-24-2013, 07:08 AM   #20
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I was ecstatic when I figured up my mileage last year. We have a 2000 Dutch Star Diesel w/Cummins pulling a 2009 Saturn Vue. We traveled from Phoenix, Az. to Alaska, then to Silver Springs, Fl. and averaged 9.75 MPG for over 9,000 miles. I'm a happy camper.
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Old 06-24-2013, 07:49 AM   #21
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So far... over 2600 miles, my average hand calculated (Gallons of fuel used / miles driven) is 10.4. I to a 3000 lb Chevy Cruze, drive 65 mph. I keep the engine brake off as much as possible to allow coasting. This is driving the Mid-Atlantic corridor (not a tremendous amount of hills).

While I'd like to have 400+ hp... the ISB @ 340 hp seems to be well matched for my 28k lb Coach. Enough power to get me there... but also provides decent fuel economy.
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Old 06-24-2013, 08:05 AM   #22
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We have 2 long trips in our 38' Allegro RED with the 6.7 Cummins motor. Philly to Key West and back we got 9.5 mpg and Philly to Charleston SC & back we got 9.7 mpg while pulling our Honda Element. Can't help but wonder if our boxy little toad helped improve the aero to get us that extra .2 mph. Usually run between 65 & 70 as traffic (and speed limits) allows.
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Old 06-24-2013, 08:12 AM   #23
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The biggest cost of fuel is punching a hole through the air. When you're driving something that has the aerodynamics of a shoe box it takes a lot more energy to shove the air out of the way. The best way to increase your fuel milage is to slow down. Double nickels will get you there and save your fuel cost. But don't forget the cost of your utilities for electric and heat (if you have a disel heater) I have a 400 hp ISL and my silver leaf system shows the average for 87000 miles at 7.1 mpg.
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Old 06-24-2013, 08:16 AM   #24
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Ditto

Quote:
Originally Posted by srh View Post
In as much as this is a topic of interest to most Class A owners, I do not think one can generalize this. Yes, it depends on one's driving habit, driving conditions, air pressure in the tires; to name a few, but it also, to a greater degree, is a function of type of Class A; for example, a King Aire with 600 hp dp would get substantially less miles per gallon than a 300 hp, 35' dp.
It is great that you are getting 9+ mpg on your Class A. I wish I could say the same about my Essex with 500 hp, over 40K lbs. and I do not expect that either!

Respectfully,
Ditto. I was pulling my hair out 'cause my old Fleetwood with a C7 Cat pulling 32K was ringing in at about 7mpg while no amount of TLC can coax our Beaver with its C13 pulling 48K down under 5.6 mpg.

Then, a buddy bought essentially the same rig, and reports mileage within a tenth of mine.

What irks me are the ones which defy the hp/weight relationship, like a Prevost-driving friend who cruises with his hair on fire and still manages to get 7-8 mpg in a heavier rig with 75 more hp than us. His Detroit Diesel is a more efficient engine, apparently. At $3.32 a gallon, that's up to $95 difference, every 500 miles. Danged!
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Old 06-24-2013, 08:51 AM   #25
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I average about 8 MPG pulling a toad at 60 MPH.
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Old 06-24-2013, 09:03 AM   #26
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Just wondering what everyone has for rearend gear ratios mine has 4:63 with a 8.3c cummins. Ratio might be a factor in the mileage factor.
So if you know your ratio post them up it should be listed in the build sheet or owners manual or the next time its serviced have the guy look on the tag on the rearend.
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Old 06-24-2013, 11:58 AM   #27
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I have very few posts but have read this site for years.
I used to be a long-haul trucker (30 years ago) My Detroit Diesel 8V71 T averaged 4.4 mpg for over 200,000 miles before I sold it. My ex-father-in-law had a 335 Cummins in his Kenworth truck. He swore he got over 5 mpg with it but when we happened to be traveling together (rarely) wouldn't you know it but we both put in the same amount of fuel at the truck stop

[moderator edit]

Our DP grosses 22K without our toad, 25.5 with it. 5.9 260 hp Cummins, Allison T-1000 trans. We average about 10.5 mpg on our trips, driving it very easy, never over 60 MPH in the Pacific NW. I hand check the mileage and fill at the same Shell truck stop near the house. Low of 9.5, high of 13. New tires, well inflated, etc etc.

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Old 06-24-2013, 01:01 PM   #28
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The old adage that "Time Is Money" holds true. I have learned to just sit back and drive between 55 and 60 on the open road. So, although it takes me more time, I have a few extra nickles in my pocket.
One time I was caravaning with a buddy. He drove at 65, I followed right along. Watched my mileage go down .4 per gallon. That's a big difference over time.
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