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-   -   Diesel Pusher MPG (https://www.irv2.com/forums/f258/diesel-pusher-mpg-427197.html)

sledbiker1 01-27-2019 11:34 AM

Quote:

Originally Posted by Piker (Post 4608059)
It's important to note that mileage can't be tracked accurately on a single tank. You have to check it over long distances and the course of time. On a large tank, you can't always get the tank to the same level depending on how flat the ground is at the refueling station. The lowest MPG that I have recorded on a single tank was 9.4 - with the highest at almost 13. Neither of those is a true representation of the actual fuel economy of the engine.

I think because of the differences in the amount of fuel I end up with in the tank at each fill up, I can't really see an accurate pattern with regard to fuel mileage for mountain driving vs flat lands cruising... though I am sure there must be a difference.

On a 7500 mile journey out west and back, our average MPG was 10.3 - but that includes the fuel used by the generator that ran 122 hours over the course of the trip. I put together a simple spreadsheet that allows me to estimate the amount of fuel that the generator uses, so I can come up with an estimate for the drive engine. I posted the results of our 7500 mile trip here: https://www.irv2.com/forums/f123/urge...ml#post3154432

FWIW... just remember that our pusher is light duty compared to what most people have. It's only 34' long, and right around 22k fully loaded... not to mention a more aerodynamic front end than most. It also has the old P-Pumped mechanical 12 valve Cummins - which has a reputation as one of the more efficient light duty diesels on the road.

cheers

I looked at your spreadsheet to see how you figured out generator usage if I'm not mistaken you chose half a gallon per hour and your generator size would be the 7.5 kW model I'm thinking, your usage was constant. I myself try to work out a number for my generator which is 7.5 kW and found the fuel usage depended on the percentage of workload on the generator I found it very difficult to come up with exact number's, it's just like guessing how many jellybeans in a jar. My rig also has 100 gallon tank with a diesel fuel gauge that reads in eighths, kind of nice as it's one big square tank makeing the diesel gauge quite accurate. So I watched fuel gauge and the load and the time over different week periods of Boondocking, it was all over the place, all because the loads very so much.

And You're right Piker, without thinking of this drainage from your fuel tank how can you accurately tell you're miles per gallon.

Just saying...

Piker 01-27-2019 01:49 PM

Quote:

Originally Posted by sledbiker1 (Post 4608857)
I looked at your spreadsheet to see how you figured out generator usage if I'm not mistaken you chose half a gallon per hour and your generator size would be the 7.5 kW model I'm thinking, your usage was constant. I myself try to work out a number for my generator which is 7.5 kW and found the fuel usage depended on the percentage of workload on the generator I found it very difficult to come up with exact number's, it's just like guessing how many jellybeans in a jar. My rig also has 100 gallon tank with a diesel fuel gauge that reads in eighths, kind of nice as it's one big square tank makeing the diesel gauge quite accurate. So I watched fuel gauge and the load and the time over different week periods of Boondocking, it was all over the place, all because the loads very so much.

And You're right Piker, without thinking of this drainage from your fuel tank how can you accurately tell you're miles per gallon.

Just saying...

Correct... I settled on .5 gallons per hour for the spreadsheet that I posted, and yes that is an ESTIMATE. There is no way to know exactly what the usage is... however, the manual for the Onan DKD generator DOES state that at max load it uses .9 gallons per hour. The .3 gallons per hour minimum that I used was not from the manufacturer. That was a number I got off of another website and who knows if it's accurate.

The fridge, and two AC's are nowhere near taxing the capacity of the generator... so I used a number closer to the lower end of the spectrum than the higher. This would skew the mileage of the Cummins downward actually.

If you change the estimated hourly usage of the generator, it changes the mileage calculation for the Cummins:

.4gph generator = 11.1 Cummins
.5gph generator = 11.3 Cummins
.6gph generator = 11.5 Cummins

Worst case scenario, the generator is actually a perpetual motion machine that uses 0 gallons per hour over the 122 hours in the spreadsheet, and the Cummins ends up at 10.3 :cool: :D

The whole purpose of the spreadsheet was basically just because I like spreadsheets... and because I was curious... and because I wanted a baseline for budgeting trips. When we plan a trip, I estimate 10mpg overall, and we've never gone over budget on fuel. :thumb:

-cheers

tropical36 01-27-2019 02:24 PM

Quote:

Originally Posted by Dan104 (Post 4591417)
Looking at 2000 to 2006 Diesel Pushers 36 to 40' long. Being I like to know what I am getting into in advance. Please let me know what MPG you are getting. Please include year, model, length, Cummins or CAT, HP, interstate cruising speed driven. Thanks

Be sure to take these responses with a grain of salt, since this subject is one of the most lied about, along with those, who failed miserably at arithmetic.
We normally cruise at 57mph and for staying in 6th gear OD over hill and dale the average shown, on our digital readout over a period of 11 years, is 6.2 mpg, which I find to be pretty insignificant in the overall cost of ownership.
In fact MPG and RVing probably shouldn't be used in the same sentence....lol
Now, depreciation per mile is another story and find this well worth noting, if it's all about money and the newer it is, the worse it is. Having said that and with the age range you've stated, you'll be better off, than many.
The good news is, that you'll never be in need of another hobby....:dance:

Piker 01-27-2019 03:35 PM

Quote:

Originally Posted by tropical36 (Post 4609070)
Be sure to take these responses with a grain of salt, since this subject is one of the most lied about, along with those, who failed miserably at arithmetic.
We normally cruise at 57mph and for staying in 6th gear OD over hill and dale the average shown, on our digital readout over a period of 11 years, is 6.2 mpg, which I find to be pretty insignificant in the overall cost of ownership.
In fact MPG and RVing probably shouldn't be used in the same sentence....lol
Now, depreciation per mile is another story and find this well worth noting, if it's all about money and the newer it is, the worse it is. Having said that and with the age range you've stated, you'll be better off, than many.
The good news is, that you'll never be in need of another hobby....:dance:

Why do I always feel like I’m being called a liar when I post mpg of our rig? I mean, I’ve been called a liar before about it, but sometimes it doesn’t actually get said... it just gets implied? That’s a question... not an accusation.

Those of you with great big 20 and 25 ton rigs will definitely not see the same mpg as us. We basically have a glorified pickup truck chassis and engine... with an oversized Allison. Talk to the guys with the dodge trucks towing gross weights of 20k... they are all getting 10 to 12. Even the duramax and powerstroke guys get that. It’s not that unbelieveable.

All that said... yes, some people tell fish stories. And still others just don’t understand the issue of tracking mileage over time. If you look on my spreadsheet, one fillup showed 13mpg. The guy who doesn’t understand that his tank wasn’t really full at that station migh think he actually got 13. Like you said, it’s an arithmetic thing... but it’s not necessarily a lie.

One more point... checking fuel economy can be like checking the oil. Might tell a story if you have a problem somewhere. Exhaust appearance might not be as helpful. When we dusted our engine, we burned a quart every 250 miles... but when I looked in the mirror I couldn’t tell.

Ok... one final... final point. Depreciation is generally a big deal on these... unless you buy a hunk of garbage like we did and pay for the depreciation in repairs. And as far as fuel mileage... for those of us with old stuff, the fuel cost is actually a very large percentage of the cost of ownership. Ok... there was an extra point in there I didn’t warn you about. Send me a bill.

Cheers

HJLowell 01-27-2019 04:05 PM

Quote:

Originally Posted by Piker (Post 4609209)
Why do I always feel like Iím being called a liar when I post mpg of our rig? I mean, Iíve been called a liar before about it, but sometimes it doesnít actually get said... it just gets implied? Thatís a question... not an accusation.

Those of you with great big 20 and 25 ton rigs will definitely not see the same mpg as us. We basically have a glorified pickup truck chassis and engine... with an oversized Allison. Talk to the guys with the dodge trucks towing gross weights of 20k... they are all getting 10 to 12. Even the duramax and powerstroke guys get that. Itís not that unbelieveable.

All that said... yes, some people tell fish stories. And still others just donít understand the issue of tracking mileage over time. If you look on my spreadsheet, one fillup showed 13mpg. The guy who doesnít understand that his tank wasnít really full at that station migh think he actually got 13. Like you said, itís an arithmetic thing... but itís not necessarily a lie.

One more point... checking fuel economy can be like checking the oil. Might tell a story if you have a problem somewhere. Exhaust appearance might not be as helpful. When we dusted our engine, we burned a quart every 250 miles... but when I looked in the mirror I couldnít tell.

Ok... one final... final point. Depreciation is generally a big deal on these... unless you buy a hunk of garbage like we did and pay for the depreciation in repairs. And as far as fuel mileage... for those of us with old stuff, the fuel cost is actually a very large percentage of the cost of ownership. Ok... there was an extra point in there I didnít warn you about. Send me a bill.

Cheers

Well your a great guy.
Keep cool.
You at least addmitted that you bought a pile of junk.
Blew the engine.
It takes a man to do that.
Regroup and move on , Enjoy.

You will learn there are things you dont discuss.[emoji23]🤣[emoji6]

Maik 01-27-2019 04:10 PM

98 Fleetwood American Eagle Cummins C8.3 w/ 3060 Trans, non waste gate turbo (32 psi) 325 hp - towing Jeep Wrangler 7- 8 mpg @ 65- 70 mph. Pushing a gross combined weight of 39,000 lbs. I could do better if I stayed between 60- 65 mph. Not retired yet so time is more of a factor.

Piker 01-27-2019 05:19 PM

Quote:

Originally Posted by John Haggard (Post 4609284)
Well your a great guy.
Keep cool.
You at least addmitted that you bought a pile of junk.
Blew the engine.
It takes a man to do that.
Regroup and move on , Enjoy.

You will learn there are things you dont discuss.[emoji23]🤣[emoji6]

Correction good sir... I never admitted to buying a pile of junk. I did admit to buying a hunk of garbage. Subtle nuance... :rolleyes:

Cheers

Damion 01-27-2019 05:55 PM

Piker's spreadsheet is GREAT!

I plan to fill up a full page on it this summer and then I be able to say what my mileage really is! Thanks to Piker's spreadsheet!

tropical36 01-27-2019 06:14 PM

To the OP and as you can see, the numbers are all over the place.
Hard to believe that so many like coaches can be that far apart for fuel mileage, too.
I for one, will only rely of some sort of a computer for calculating my average and for over long periods of time.
We are the third owners of ours, which had an average of 6.1 when purchased.
In the last 2 1/2 years I've only been able to improve on this average, to 6.2, with my style of driving.
What I've never bothered to check, is if it's on the tank or the engine and if the genset, is being included, also. I'd venture to say it's the former and what the total fuel usage, actually is.
As a side note, the best way to save money on fuel, is for staying over at a Walmart on occasion. ÖÖÖÖ..and no, I'm not trying to start a Wally World War, here....:nonono:

sledbiker1 01-28-2019 08:47 AM

I thought I might throw one more in, has you see, I use sledbiker, it's because I like snowmobiling and motorcycling they both weigh under 700 pounds they both have four cylinder four stroke engines on the snowmobile I get 11 to 14 miles per gallon and on the motorcycle it's better a lot better like three times better, I guess a lot of it is because of friction and drag. Anyway it's not because of the miles per gallon it's because of the Smiles / Miles... And that also lead me to believe that RVing would be the same and you know something it is...

The thought of burning a gallon of fuel, makes me think, about the same way as cooking a T-bone steak... And don't forget the beer...

Just saying...

CA-cruzn 01-29-2019 08:53 AM

We just returned from our madden trip and I was surprised that we got just over 10MPG! We were not towing and put a total of 335 miles on the coach. We just bought a Fleetwood Discovery 37T with a 330 HP Cat with 50,000 miles on her.


Robert and Jackie

lowhut 01-29-2019 04:28 PM

You don't buy a diesel pusher if you are concerned with mpg. Just fill the tank and go and enjoy. Most will get right at 8.

stevewitt1 01-29-2019 08:19 PM

Wow: I guess after reading most of these replies I now understand where the saying:


RESULTS MAY VARY AND PAST PERFORMANCE IS NOT AN INDICATION OF FUTURE RETURNS, LOL.



I bought a 2008 Fleetwood Bounder 38F with a 6.7 ISB Cummins 350hp engine and Allison 3000 trans. This power train won't necessarily give you whiplash when you step on it, even going down hill but the mileage has been decent. I have the DP and maybe I'm the modest income or net worth DP owner but mileage is important to me. Maybe I'm so pathetic that getting better mileage is the cheap thrill I enjoy at this ripe old age. Enough about me. I bought it with 29K miles on it in 2016 and have 40K and change on it now. I didn't get real fancy as Piker's spreadsheet which I'm really envious of but over the first 10,000 miles I used almost exactly 1,000 gallons. (I do keep a log). That included about 160 hours of generator time with my Cummins Onan 8000 genny. My mistake was I thought when I looked up the engine I read 1,700 rpm was peak torque. Last year my daughter the bought me my ScanGauge-D and I found out I'M BAD!!!! I looked up my engine again and found out 1,500 rpm is peak torque. While driving those first 10K miles I drove approx 61mph on my GPS which ran my engine around 1,720-1,775 rpm on the dash tach. Now I run 1,520-1,575 rpm which shows me around 55-57 on my GPS but has brought me between 11.6-12.5 mpg. I haven't make a long cross country trip since the change yet. The longest have been around 175mi legs. Hopefully, next month I'll take off for Yuma from here north of Green Bay and get a good idea of the trip performance. Maybe I'll be happy, maybe not. 8-9mpg isn't the end of the world but I enjoy getting better. I enjoy dry camping on my trip as much as possible while traveling. I guess, I'm sorta cheap, LOL.
Steve


[moderator edit]

Powerstroke2000 01-29-2019 08:39 PM

Good for you, nothing wrong with being anal about wanting to know fuel mileage, or any other portions of motorhome services. Since we tend to go and want to get from A to B on whatever fuel the motorhome takes..so be it, but I'm one to travel at 60 mph pretty well all the time, as I don't believe we should be in a huge hurry now that retirement has arrived, as well as it's overall being safer to drive slower generally. Thanks for letting us know of your setup, and let us know when you find if your better mileage stays similarly if/when driving mountain regions as well. Always nice to know if most DP's are getting similar mileage, as I have the 360 HP Cummins in mine. Hard to believe my diesel pickup is set up win well over that HP in a much lighter vehicle, but the way the torque is set up with the Allison 3000 it seems to do just fine on hills even with towing.


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