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Old 12-07-2011, 02:33 PM   #43
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Rough Road - I guess I travel different highways than you do. I believe I'm passed by as many or more "C's" and 5th wheels than I am by the larger A's. Yes I do get passed by the bigger guys as well as the smaller ones since most of my highway speeds are 58 to 62 mph. I do take exception to your comment "all Class A mpg reports are 100% Class A tall tales". I have tracked every gallon I've put in my RV and come up with 7.8 mpg on my 30K plus miles. I tend to agree some or many claimed mpgs are not the fuel average for the vehicle. I once got well over 9 mpg on one tank - with a Strong following wind but that is not my average mpg.
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Old 12-07-2011, 05:41 PM   #44
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1ciderdog, did not intend to offend but I meant what I typed, your mpg report is, to me, is in line with what I would expect from a Cummins 300/350 in your application ?, could you tell me how you check your miles per gallon??

I, by the way, drove our old Shasta slowly also, that 460 consumed breathtaking amounts of fuel, but would you agree that we are perhaps two of the four people in the entire universe that drive/drove motorhomes in the manner in which we did???

Have at me all, but the bigger the rig the faster it is driven, yes there are exceptions as 1cider types-but the exceptions are few and far between-I and the dw have never ever observed an A being operated at anywhere near the posted speed.

Fuel costs were and will be a big concern for us-isn't it fair to say that the more wealthy among us don't have to be concerned with getting another few miles per gallon by traveling alot below the limit?

And to be clear, I am happy there are folks in that position, and in fact I do wish I were one of you....but I ain't and I ain't ever gonna be so I gotta drive real slow.
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Old 12-07-2011, 06:36 PM   #45
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Rough Road, I actually check the mileage every time I fuel up. I keep a log using odometer mileage and fuel put in. Sometimes I get 6.5 or so mpg on a fill up but that is usually after I've had a real good mpg on the previous fill up. I've entered into an Excel spreadsheet all the dates, miles, locations and gallons for each fill up and have come up with the overall mileage as 7.8. No adjustment has been made for when I towed or used the dash A/C or generator. The mileage was over mountains and flatlands all around the US and I think is a true representation of the actual mpg of that coach the way I drive it. The odometer for the motor home is very, very close to the mileage traveled as shown by the GPS. In the mid 1980's I had a 1976 Vogue Motor home with the Dodge 440 and the three speed transmission. It was much smaller and didn't weigh nearly as much as my present motor home. It consumed a considerable amount of fuel - I don't remember the average but by memory I was happy when it exceeded 6 mpg. Like you I tend to not give a lot of credibility to the 10 plus mpg some RV'rs say they are getting.
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Old 12-07-2011, 06:45 PM   #46
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Have at me all, but the bigger the rig the faster it is driven, yes there are exceptions as 1cider types-but the exceptions are few and far between-I and the dw have never ever observed an A being operated at anywhere near the posted speed.
Not true at all. We are on RV number five and have cruised all of them around 62/63. I'm sure this big Cummins would run all day at 75, but the slower speed is much more relaxing and the MPG is tolerable. We've travelled in convoy with three others, our consensus is that 62/63 is a speed we can all be satisfied with.
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Old 12-07-2011, 07:01 PM   #47
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OK OK all you with a Hydro-Hot and Aqua-Hot. If you want to know how much fuel it uses, figure it has a .35/gph nozzel. Figure it out yet? Also, with the Cummins engine all you have to do is hook up the Insite program and it will tell you exactly how much fuel you have run through the engine from new.
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Old 12-07-2011, 07:13 PM   #48
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To me 8mpg on a Cat C7 is wishful thinking over the last 5 years running to Maine in the summer and Florida in the winter pulling a Jeep GC I've gone from 6.5 -7.7 I run 58-65mph use the generator on hot days, have 38k on the engine had the valves adjusted, ECM flashed with the latest updates, it is what it is. Wish it was better, glad it's not worse.
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Old 12-08-2011, 07:31 AM   #49
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hondo, what impresses me is that the diesel A's are able to even get what they do considering the work the engine is doing.

For a number of reasons diesel is the only way to go in any class rv.

Bob, 6 or so was about what the 460 got us-roughly ten gallons per hour imagine $36.00 per hour just for gas

Come to think of it we haven't seen any of those ridiculous 'how economical the rv vacation is' ads in a very long time.
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Old 12-08-2011, 09:41 AM   #50
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Running a 450 ISM Cummins on my 40' Monaco I average around 7.7 MPG and tend to run around 70 towing 3200lb trailer.
I use the Odometer/gallons over many fill ups and thousands of miles including dry camping to get to that number. Aqua hot does eat some fuel as well as the 12.5 Onan If just running down the road and not dry camping or running the gen it will peak around 9.20 MPG at it's best. Worst case is a short trip dry camping, say 400 miles and 2 days with Gen running and aqua hot on, closer to 3.9 MPG for that trip.

But like Rough Road points out, the average is the average, not the best you have ever seen. So many people see a number they like and that becomes the number for every case...
Also, pointing out the mileage indicator on the dash and using those numbers. Sorry def ears on that one from me. It might possibly be correct but dout it tells the real story.

Don't forget that warming up, starting off and the first 50 miles or so things are coming to temperature so your mileage will suffer the more you stop overnight.

Based on what I have seen, the larger engine models can be operated efficiently but not without having to restrain yourself on those hills and such.

Drivers make a big difference also. My wife tends to be on the gas, off, on, off... rather than being able to find a happy throttle position to maintain. This on off stuff eats fuel (and is annoying). Getting the Turbo spooled up for a hill just before you hit the hill helps (unless you are ok with loosing speed on the hill) because you don't loose any momentum causing you to have to dig even deeper into the turbo to regain your speed.

Tag axles eat fuel also, from what I have been told, about 1 MPG over non tag units.
Sorry for the long read!
I really enjoyed reading all the previous posts.
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Old 12-09-2011, 06:11 AM   #51
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windecker, what is the sweet spot-those revs where the engine just sounds as though it could run forever, not too fast nor slow- for your Cummins, speed and rpm, and if you operated at that point how do you think the mpg would change, both towing and not towing-and just out of curiosity what is the tach rev range for your engine?

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Old 12-09-2011, 07:29 AM   #52
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On the highway the engine seems pretty happy above about 62 or so but really loves it around 70-75
For me having a non wastegated engine it seems to like a few more RPM's to give me snappy turbo boost and full boost at that.
I think 65 is right around 1530 RPM and 70 is sneaking up on 1600 RPM and 75 is sneaking up on 1700 RPM, maybe just short of it as I recall. I don't Drive 75 unless I am on a long trip and out west... That speed will cut into the mileage a bit and is approaching unsafe speeds IMO.

I worked hard this year to keep the speed down and try to drive around 65 which may have helped the mileage a little but honestly not much in the overall picture.

Also I found that it pulls the smaller hills here in the midwest pretty well at 63-65 which I was not expecting because I can only get about 25-27 PSI of boost at that speed. Above 72 and I get full boost, pegs the meter at full which is 30 PSI and it just goes.

All that said, off the highway 45-55 MPH at 1350 or so it sounds really sweet and seems as you say like it could run forever. I only drive that way on one route I take and it gets the worst mileage of any I do a year. I suspect it is because of how many stop lights and traffic I have to deal with rather than the speed/RPM.

Honestly the only time it seems unhappy is while upshifting around town as it upshifts very early like around 1200-1400 RPM, right after upshift it lugs a bit as it will only be turning roughtly 1000 RPM.

Sorry for the long read, I just can't explain things like others can with few words.
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windecker, what is the sweet spot-those revs where the engine just sounds as though it could run forever, not too fast nor slow- for your Cummins, speed and rpm, and if you operated at that point how do you think the mpg would change, both towing and not towing-and just out of curiosity what is the tach rev range for your engine?

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Old 12-09-2011, 03:48 PM   #53
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In my first long trip from Orlando to Dallas I got 7.4 mpg.
To fill I would level the coach and fill to the neck on the drivers side each time.
I have a Monaco dynasty with full water tanks and tow a Subaru outback.
Engine is ISC 350 cummins
I generally travel between 60 - 65 mph increasing to 68-70 mph to at least try to keep up with the crazy texans
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Old 12-09-2011, 07:22 PM   #54
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windecker, I was expecting low revs but not as low as you report; your engine isn't working very hard at all-impressive.

steve, about what revs are you seeing at the speeds you mention?
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Old 12-09-2011, 07:37 PM   #55
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Mr. D, I can assure you that if you fill your tank to a level in which you can see the fuel, drive anywhere you wish over any type of terrain/grade you wish and refill to the same level in the neck it did indeed take you whatever amount of fuel you put back in to travel the distance and roads you traveled-this you can take to the bank.

No you will NOT get the same mileage on a flat road as going up grade and I never inplied any such thing, but you will get the same mileage going up the same grade every time; all things being equal of course.

You in all probability won't like the numbers you see but as in many instances, the truth is unpleasant.

Please don't read anything into this, I really do like you class A folks and I really do like looking at what some can spend their money on, but knowing what I know about punching huge holes in the atmosphere with very large and very blunt vehicles 99.99% of all Class A mpg reports are 100% Class A tall tales; by people who really really want to believe the skewed numbers they come up with.

What we see while traveling is this, nearly all Class A drivers are operating significantly over the speed limit-and thats fine by me- and all Class A drivers seem to be hell bent on proving that their magnificent motor homes can also maintain those speeds up any grade,( ESPECIALLY when someone lower on the rv foodchain is ahead of them-admit it guys you KNOW I am right) under these circumstances I know it impossible to acheive any mpg number over the mid to lower:upper single digits in the class vehicle under discussion.

Add in the 'toad' (two come to mind, one lucky guy or gal was pulling an H1 Hummer another was pulling a Land Rover Defender) or typical Class A 'trailer' and I don't see any number over 6mpg possible, even down the longest grade on the planet.
Sorry about the chip on your shoulder regarding Type A MH's and their owners. I can assure you, you're wrong.
BTW: those figures I quoted were more for fun than anything as those are instantaneous readings and NOT averages. I was trying to show how rediculous the figures given are. But they ARE the actual figures I have seen while traveling. I've seen everything from 2 mpg to 256 mpg depending on the terrain, speed, wind, etc.
I get passed all the time by 18 wheelers, and gas MH's. The worst are the 5th wheelers towing at 75 mph when the speed limit is 60 for them here in WA. I can hold over 90 mph if I want but I don't. In fact I can go faster if I want to bump up against the rev limiter.
Running at 60-62 MPH I'm not even at my HP peak now that I have the Banks kit on, and I'm only part way through the torque curve which starts to fall below 1200 ft lbs at 1700 rpm.
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Old 12-09-2011, 09:02 PM   #56
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I've got 1700 at 60- 62
And from memory 1800 at 70 mph
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