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Diesel Motorhome MPG-- Honest Answers Please

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19 hours ago, fagnaml said:

The engineer in me is curious how Freightliner and other motorhome chassis fabricators decide how to "mate" engines and transmissions

Id bet it's torque/RPM related, 6th gear may drop your rpms but would a 5.9L have the torque at that RPM to push that unit is the question? If so can it do it without creating excessive emissions also, think about it if the engine is lugging its polluting and not saving you a dime. Manufactures are always trying to match up the engine "sweet spot" to the remainder of the powertrain. The 3000 series is a larger heavier unit which will also absorb more of your HP and torque before it exits the transmission. Usually you have to cross a specific HP and torque threshold before the next transmission size will be a standard or even an option.

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Classic example -Tiffin RED. Initially available with a 340HP ISB and an Allison 2500. A 360 HP ISB, an Allison 3000 and higher rated axles became an available option, on the same chassis. That became what everyone wanted, so for 2017, no more 340HP and Allison 2500! The buyers are willing to pay, so that's what Tiffin gives them now!

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I just read a few of the more recent posts. For many years now I have kept a fuel log on my laptop. I log the miles, gallons used, cost of each fill, then using excel I calculate current tank, 4 tank, 10 tank and lifetime average. Should I get a weird reading I know that something is up. I also link the spreadsheet to a log where I record trip highlights. So here is my last trip 1966 miles at 9.08MPG. My dash computer says I should have gotten 9.7. The first tank out I showed 10+ on the dash, later I dropped down to 8.9.This got me to wondering about B20 and other mixed fuel. I believe my 1st and last tank were both straight diesel, the two in the middle were B20. Does anyone else see B20 having an adverse effect on mpg?

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16 hours ago, Concrete200 said:

Just went Arkansas-Florida-Arkansas and had an average of 5.6 mpg pulling a jeep.  600 hp Cummins pushing an American Eagle. 

Welcome to the forum. Not that bad for that coach. What speed do you cruse at?  

Bill

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It depended on both road conditions and traffic...70 in a few areas where the traffic was sparse and the pavement was smooth...60-65 on the majority of the 4-lane non-limited access highways...

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7.5 mpg overall on our last trip to CA and Oregon from Denver.  We have a 2013 Itasca Meridian 42E with tag axle (44K GVWR) 400 hp 8.9L Cummins ISL with DPF and Allison 3000, cruising 70-75 and Onan 8000 running at least half the time and a 97 TJ Wrangler (~3,500 lbs) on the back 4 down.  

DEF consumption was within the Cummins guidelines, but I was a little shocked at how thirsty that exhaust filter got.  I can't remember now but I think we used 10 gallons over 3,800 miles.  My pickup would have used 1/4 of that in twice the mileage.  It guess its all about the size of the filter.

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Just filled the coach up and to my surprise our MPG was 9.4, during that time I had the generator running also that totaled 42 hours on this tank and Jeep in tow.

Our trip to Florida in the end of June we were averaging 7.8, I could feel the headwind which felt like I had it from PA to FL. 

I am completely satisfied with this!!

I have noticed the new tires have been a help keeping my RPM's lower since they are taller and now all 6 are smartway certified which I didn't have before.

At one point on this post I had clocked 10.05 before on an all flat ground trip to MD from PA, smaller Toad on that trip. Unfortunately when we did the same trip this year I didn't clock our MPG. 

 

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18 plus MPG... YES, no kidding... even climbing mountain grades.. 

Go ahead... take a look at my rig... it's true...

I might be able to get 19 or 20 on flat areas cruising on the road...

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15 hours ago, MWeiner said:

Yes, very aerodynamic... fuel is the MOST expensive thing you put in a vehicle over time.

While true-- fuel is certainly an expense, depreciation well out-strips all other costs of ownership.

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On 12/1/2016 at 11:37 AM, fagnaml said:

Wildebill --

The engineer in me is curious how Freightliner and other motorhome chassis fabricators decide how to "mate" engines and transmissions.   A what engine size would Freightliner decide to use a six speed transmission (e.g. Allison MH-3000) rather than a five speed transmission (e.g. my Allison MH-2500)? 

 

It's a numbers game.  For MHs, when considering the Allison 3000 and 4000, it all depends on HP and torque.  The cut off is 450 HP and 1250 ft/lbs of torque, if that or less you get a 3000 if more, you get a 4000.  I found it interesting that they ignore the weight....HP and torque are the only criteria...you can tow any thing you want to tow.

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1 hour ago, rossboyer said:

I agree with Brett. Last year my total expenses was $1.54 per mile of which 60% was depreciation. 

Yes, I agree to a point...and depreciation is WHY I purchased a five-year old coach with very low miles, but, remember that depreciation is only important if you intend to sell.

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7.5 - 10,  Coach + Toad on trailer weighs around 37000. MPG is figured fillup to fillup and not adjusted for generator, hiway or intown, mountian or flat, wind or no wind and I usually drive the speed limit or a couple over. It is what it is. There have been thousands of dollars spent to get 1/2 mpg increase and if you want bragging rites then go for it

On a year to year figure I believe fuel in most cases will be one of the least expensive costs of ownership.

Just my two cents

Gary

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4 minutes ago, garyreed said:

7.5 - 10,  Coach + Toad on trailer weighs around 37000. MPG is figured fillup to fillup and not adjusted for generator, hiway or intown, mountian or flat, wind or no wind and I usually drive the speed limit or a couple over. It is what it is. There have been thousands of dollars spent to get 1/2 mpg increase and if you want bragging rites then go for it

On a year to year figure I believe fuel in most cases will be one of the least expensive costs of ownership.

Just my two cents

Gary

Gary, 

Depends a lot on how far you drive.. 10 MPG difference is a really big cost factor.

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I agree with you MWeiner,

The better the MPG the more cost savings per year or mile how ever you want to look at it.

When a person looks at purchasing an RV all the numbers need to be looked at and the right RV must be selected on what you are willing to spend including the purchase price.

In the 80's and 90's my parents traveled the country in a Toyota Chinook, similar in size to your's, it also got 15 + MPG and served them well. They also had no kids, pets or toad and when they needed to take their Bronco II my mom drove it which added to the expense. 

I am not knocking anyone for their preferences on what they want or can spend, or what the choose to drive.

My analysis may be simplistic, but works for me. Expences for the year: propane, fuel, oil, insurance, camp grounds etc. compared  to expenses for the same number of nights including gas, oil, flights, car rentals hotels etc. I then factor in the comfort I get from sleeping my own bed and using my own toilet, taking the dogs, and the sights that I might otherwise miss. The RV will win out 99% of the time.

We are going to travel whether we use an RV or a hotel room so it boils down to want for your money vs what you get for your money.

If it was only the money, I would drive a Volt or Leaf or something and sleep in a tent.

Gary

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Yup, first "RV" (I use that term lightly) got 28 MPG-- a 1958 VW panel truck I bought for $150 with household furniture.  Would I go back-- no way.  Would my better half go THAT FAR back-- you have to be kidding.

As those of you who know me, I do monitor MPG.  Is it the overwhelming factor in selecting and operating a motorhome? Not a chance.

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5.75 mpg average .... lot of traveling over mountain passes drags it down quite a bit.  I didn't buy it for fuel economy.  42foot, quad slide, 525 HP CAT.

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Bill,

Is your 92 a silver? I have worked on those in years past and still love the way they sound today.

Wolfe10,

My first Rv experience was at seven or eight  in the early 70's and involved a 57 Chevy bus convert and our friends had a 50's cadillac front end and some kind of a camper mounted on the back. the other friend had a early 60's GMC pickup with an overhead camper and that humungus V6. And those were some  very happy memories and I to would not want to go back.

Gary

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