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Old 11-18-2017, 09:22 PM   #15
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Well Gang,
First off, for the life of me, I can never understand why ANYONE, who's ever considered purchasing a rolling KLEENEX box that weighs anywhere from 25K to 60K lbs and has the aerodynamics of a BRICK, worries about fuel mileage. They're gonna get what they're gonna get, period. From talking to folks at campgrounds across America, with multiple varieties of motor homes, especially larger diesel ones, the majority get what we get, around 6.5 - 7.5.

We just got back today, from a 52 hour, 2,100 mile trip from Ohio to Lake Havasu City AZ where a buddy of mine picked up a '14 American Revolution with 10K miles on it. It has the ISL 450 Cummins. We fueled it three times and put 7 gallons of DEF in it during the trip. The on board computer consistently reported 7.1 to 7.3 mpg. It's 43' tag axle coach with around a 46K GVWR.

He get's the same mileage I do with our '04 Itasca Horizon 36GD with the C-7 330HP CAT, about 7.1, plus or minus. If I worried about fuel mileage, I shouldn't have one of these rolling gymnasiums. I and all my traveling friends have them to enjoy them and go places and meet people with the same interests and see and do things.
Scott
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Old 11-19-2017, 05:16 AM   #16
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Getting better MPG is a game. Something to do driving boring Interstates. Why pay gas companies more? Why pollute more?
2 V10s 8.9 and 7.9 mpg "No tows."
My 380 Cummins 8.9 mpg but 50% more weight. Pulling my Accord. 10 mpg no tows. Diesel climbs hills much better than gassers.
I monitor fuel economy because I was brought up to conserve. Something dead/dieing in the country.
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Old 11-19-2017, 05:53 AM   #17
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No, wasn't pondering an upgrade - I haven't squeezed the Buffalo sufficiently on our current rig. But I must say you are putting a dangerous idea in my head. :-)
I might be reinforcing or bringing the idea forward but I think it was there subliminally. Be careful or you will start cataloguing faults in your current RV and starting an advantage and must have list for a new one. At least that's how my brain works.
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Old 11-19-2017, 06:01 AM   #18
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Thanks to all who have responded. The purpose of my question has to do with mechanics and technological progress of diesel engines. If I was really concerned about mpg, I would not have bought a MH (or any RV, for that matter). :-)

That being said, having no appreciable decrease in mpg, while at the same time substantially decreasing pollutants, is progress. Thanks to those who pointed out this factor. You have increased my knowledge.
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Old 11-19-2017, 06:24 AM   #19
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I just traded in a 1998 Dutch Star 38' DP with the 300hp Caterpillar 3126b engine. Fully loaded (27,400 GVWR) and pulling a Jeep about 75mph with the generator running and air conditioners going we would get about 8.5, but that also includes running the generator at night.

Just got a new Cummins 360hp in a 32k GVWR 33' Tiffin, and have yet to make any trips. I'll be interested to see how it compares.
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Old 11-19-2017, 07:09 AM   #20
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Diesel mpg actually went way down in 2007 with the [mandated] introduction of new pollution control gear, but went back up again in 2010 with the change to SCR (the technology that uses DEF to scrub the exhaust). I think the net is that a post-2010 rig gets about the same mpg as a pre-2007 did.

Rigs in the 2003-2006 era seem to do a bit poorer than their predecessors, but weights, lengths and engine sizes were also increasing rapidly in those years so it's hard to get an apples-to-apples comparison.

My 2004, which had a 2003 ISL 370 and weighed in around 37k lbs, averaged 8.1 mpg over several years. A large proportion of that was interstate cruising - the mpg suffered a lot if I couldn't cruise at 62-64 for hours at a time. Even light traffic on 2-lane roads seemed to push it down to around 7.2-7.4
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Old 11-19-2017, 07:16 AM   #21
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All of the EPA Crap has killed any gains the Engine manufactures may have made, and is the Reason Caterpillar stopped making engines for highway use. The only way to improve your MPG in a big Class A is to Slow down, I see them every day running 80 MPH across I-40 here in Arkansas. and I doubt they are worried about MPG
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Old 11-19-2017, 07:39 AM   #22
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Never owned a DP (YET).... I would think something that might be a advantage for a older coach is they might not have as much frontal area for wind drag. Not as tall or wide and also not as much weight to move around thus better fuel economy.

I know with my last gas coach, similar fuel economy (08 vs 97 vs 85) however 4-10ft longer, +/- 2 ft higher and a bunch more weight.

My x inlaws would get approx 8mog on their 09 40ft Discovery

The smaller 33-35ft DP like their excursion frommjust a few years ago some state 10-12+ mpg. However it’s shorter, lighter and lower vs most other coaches.


All the points you make are generally true. Fuel economy with a diesel coach breakdown into either the physics of moving weight and volume through the air or driver skill & technique.

If you look for a coach older than about ‘02-‘03 (no EGR system) and a Cummins ISB then you can enjoy max fuel economy. In those years the ISB was the undisputed economy champ in motorhome service. The rest is up to you. Limiting your speed to a range which will enable your engine to operate within a couple of hundred rpm of max torque without downshifting with every small up grade is important.

You need to keep this in prospective however. You are chasing a max of 1-2 mpg and over the course of your motorhoming experience there are lots of other important issues. No matter what you end up with, it can be fun to try squeezing the best mpg possible out of your equipment.
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Old 11-19-2017, 12:45 PM   #23
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Well Gang,
First off, for the life of me, I can never understand why ANYONE, who's ever considered purchasing a rolling KLEENEX box that weighs anywhere from 25K to 60K lbs and has the aerodynamics of a BRICK, worries about fuel mileage. They're gonna get what they're gonna get, period. From talking to folks at campgrounds across America, with multiple varieties of motor homes, especially larger diesel ones, the majority get what we get, around 6.5 - 7.5.
As for this thread its not about getting the most fuel efficient coach, the OP was curious about how engine efficiency has improved over the years.

I do not recall seeing a post where people are worried about the fuel economy, maybe I missed it?

Myself I do not have a unlimited budget thus I have always looked at fuel economy numbers. When I would plan a trip somewhere.... I would have to consider how much money I will spend on fuel to get there in addition to all the other costs. Maybe you just have so much money in the bank that it doesn’t matter to you but for myself and possibly others, I need the general idea of how much $$$ in will cost me to travel. Having a mpg number also gives me a idea of how far I can go before I am on empty

However the biggest reason I use mpg numbers is so I can get a idea of if something i is wrong. If I drive in a similar manner however the fuel economy drops say 2mpg.... I know I need to have it looked at. On my last car this happened to me, dropped 4mpg and it ended up being a faulty O2 sensor

It’s kinda like feeding dogs or cats. Some (like my parents) would keep the dog or cats food bowl filled up all the time and never paid any attention to how much food was or wasn’t eaten every day. Myself I feed morning and evening a set amount so I know if the pet isn’t feeling good, time for a checkup. Same with the RV.... major drop in fuel economy time for service.....
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Old 11-19-2017, 01:13 PM   #24
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Not a comment to the OP's thread but I know my MPG is somewhere between 7.1 at the worst and 7.6 at the best. All depends if I drive fast, pull a toad or in the mountains. I always compute my distance then figure in 7.0 MPG. I never worry about how much fuel to empty because I never ( I know never say never) let it get below 50 gallons remaining. 52 years of flying has taught me the importance of fuel management. In aviation the two most useless things are runway behind you and fuel on the ground. Jim E. OKC
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Old 11-19-2017, 01:27 PM   #25
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Well Gang,
First off, for the life of me, I can never understand why ANYONE, who's ever considered purchasing a rolling KLEENEX box that weighs anywhere from 25K to 60K lbs and has the aerodynamics of a BRICK, worries about fuel mileage. They're gonna get what they're gonna get, period. From talking to folks at campgrounds across America, with multiple varieties of motor homes, especially larger diesel ones, the majority get what we get, around 6.5 - 7.5.

We just got back today, from a 52 hour, 2,100 mile trip from Ohio to Lake Havasu City AZ where a buddy of mine picked up a '14 American Revolution with 10K miles on it. It has the ISL 450 Cummins. We fueled it three times and put 7 gallons of DEF in it during the trip. The on board computer consistently reported 7.1 to 7.3 mpg. It's 43' tag axle coach with around a 46K GVWR.

He get's the same mileage I do with our '04 Itasca Horizon 36GD with the C-7 330HP CAT, about 7.1, plus or minus. If I worried about fuel mileage, I shouldn't have one of these rolling gymnasiums. I and all my traveling friends have them to enjoy them and go places and meet people with the same interests and see and do things.
Scott
A "rolling KLEENEX box"?? Surely you must have met my wife somewhere along your travels and I didn't know about it??
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Old 11-19-2017, 01:39 PM   #26
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All of the EPA Crap has killed any gains the Engine manufactures may have made, and is the Reason Caterpillar stopped making engines for highway use. The only way to improve your MPG in a big Class A is to Slow down, I see them every day running 80 MPH across I-40 here in Arkansas. and I doubt they are worried about MPG
I for one am glad the EPA has crap. I remember the times when diesel buses would pull away from the curb leaving thick choking cloud of smoke behind. In the road construction industry the construction sites would be a haze of diesel smoke making surveying near impossible until the lunch time shutdown of equipment. It's a wonder I am still alive! Ah...they were the good old days!
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Old 11-19-2017, 02:52 PM   #27
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Myself I do not have a unlimited budget thus I have always looked at fuel economy numbers.
Sure, but the difference between 7.2 and 8.0 isn't gonna make or break the trip. The mpg is dismal, from a cost standpoint anyway. If you wanna drive a big rig, you have to bite the bullet. You can get 14-16 mpg in a motorhome, but not in a 35-45 foot class A. That fact has not changed appreciably in the past 15+ years.
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Old 11-19-2017, 07:55 PM   #28
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Sure, but the difference between 7.2 and 8.0 isn't gonna make or break the trip. The mpg is dismal, from a cost standpoint anyway. If you wanna drive a big rig, you have to bite the bullet. You can get 14-16 mpg in a motorhome, but not in a 35-45 foot class A. That fact has not changed appreciably in the past 15+ years.
If that .8 mpg is going to break the trip then yea..... shouldn’t have a RV... or that large of a RV.... for me it was more if I am going to drive x hours, miles and spend ??? On gas, I need to extend my stay xx days to make it worthwhile.

.8 mpg drop on my last coach would be making it to the next gas station or not in certain areas.

Most people are just curious about mpg, not the end all deciding factor in RV ownership, just something to talk about.
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