Back when we had our MCI bus conversion, I always felt like the red headed stepchild in the family, because every bus owner I knew claimed he got 8, 9, or even 10 miles per gallon, while I was lucky to squeeze a shade over 6 MPG from our old 8V71 Detroit diesel. On flat land, with a tailwind, we occasionally got a tad over 7 MPG, but there’s not all that much flat land in America, and we all know that tailwinds are about as elusive as honest politicians.
When we bought our 2002 Winnebago Ultimate Advantage, with its 350 Cummins turbo diesel and Allison six speed automatic transmission, RVers with similar rigs told me that they got 8 to 10 miles per gallon. Our rig only had 33,000 miles on the odometer when we bought it, so when our Silverleaf VMSpc engine monitoring system reported that we were only getting 7 MPG, everybody told me that once we got 50,000 miles on the clock and the engine was broken in, we’d see an improvement. We haven’t.
Greg White has the same engine and transmission, on the same Spartan chassis, on his American Eagle diesel pusher. Both rigs are 40 feet long,and weigh close to the same. Greg’s coach is a 1999, and has more miles on it than ours does. We tow a Ford Explorer with two kayaks on the roof, and Greg tows a four door Dodge Dakota pickup with a camper shell on it. On trips we’ve taken together, Greg consistently gets a mile or more per gallon than I do. Why is that?
I know that driving habits are usually the single-most thing that affects fuel mileage. On the open highway, I usually travel at about 62-65 miles per hour. I’ve tried staying at 55, but to be honest, I have not seen any significant difference in our fuel economy, and I get tired of the eighteen wheelers climbing up my tailpipe.
Don’t get me wrong, I’m not complaining. Though I’d love to get 10 miles per gallon like so many RVers claim to do, my home on wheels still gets better mileage than the houses most people I know live in! 🙂
But I am curious; what do you drive, and what kind of mileage do you get? And what is your average cruising speed? Have you done any modifications to your RV to increase mileage or horsepower (Banks exhaust system, engine chip, high performance air filter)?
Thought for The Day – None are so old as those who have outlived enthusiasm. ~ Henry David Thoreau
We have a 2010 Tiffin Phaeton, 40′, Cummins 360 hp ISC, Allison 6-speed and tow a 2001 Honda Accord. Usual driving speed is 62-65 MPH. Have 6600 miles on the rig so far. Silverleaf VmSpc indicates 8.3 MPG overall since new.
Gosh Nick…..you’re asking a lot here! I’ve hidden the fact that my Tiffin Phaeton only gets 6-7 mpg, now you want me to admit it out in the open to these guys claiming to get 10-12 mpg……JEESH!
I too only travel at about 63 mph, tow a Jeep Liberty, have thrown out all excess baggage, and only travel with tail winds. If I would get 8 mpg I would be shocked.
One parameter I have trouble with is I can’t fill the tank to the same level each time. Using the automotive style “fill gun” I can get several more gallons in the tank. Probably 7-8 more $4 gallons. I don’t have a spiffy Silverleaf machine, so I can only compute mpg mathmatically, so number of gallons is significant.
I’ve almost quit keeping track of miles/gallon……I give up!
We drive a 95 Coachman Santara Class C and tow an ’03 Saturn wagon. We keep it around 60-65 on the highways. This year is the first time we really drove any distance and calculated the mpg to be between 7 – 7.5. It is what it is. I’m sure there are ways to improve it slightly, but we’re happy as long as we’re rolling.
But Nick, haven’t you heard the phrase, “…I swear, the fish was *THIS* long!”
We have a 2002 Safari Serengeti 40 ft MH with the same Engine and transmission as you do, 350 hp turbo-charged Cummins with the Allison 6 speed.
We travel at 62-65 MPH range also.
Pulling a 2005 Saturn Vue and get 8 miles per gallon
Have over 60,000 miles on it and didn’t see much difference after 50,000.
The single biggest mpg killer is to drive a diesel like a gasoline engine. This means let the torque get the job done… in time.. and stop trying to “keep up” with the four wheelers.
The biggest guzzler is “too much too fast” on the accelerator. I know, I know, some people are just not compatible with torque managed driving. The SilverLeaf has the ability to set a target performance range and you can monitor it to see just how overly aggressive you might be in startup and speed change situations. Do it gradually and it will make more difference than just what speed you choose to cruise.
Every diesel engine and drive train has a “sweet spot” for the best performance. This is partly due to the fixed aspects, like gear ratios, tire pressures, etc. and partially due to the computers that manage all of this. All ECM controlled diesels can be performance adjusted by technicians to run power or run performance or somewhere in between. Most are factory set to meet Emissions requirements, first and MPG needs somewhere down the power curve. A retune might be in order to improve your MPG.
A diesel sweet spot can be fairly narrow, too, and can be drastically affected by not only the wind but the road surface. Simple example is the road going into Manteo, NC from the west compared to the road (highway 12) going down the outerbanks to Cape Hatteras. There is a good 1.5 to 2 MPG difference at the same speed on these two roads under windless conditions.
So, Drive it like the muffler fell off and you are trying to avoid getting a ticket for noise violations is a simple rule of thumb. Be sure tire pressures are high enough and watch the torque curve when changing speeds. Beyond that, performance tuning might be in order since you dont seem to ever have any issues with power in the mountains. Maybe some of that extra power can be returned to you in the form of better MPG.
Good luck with that.
We purchased a Tiffin Allegro Bay FRONT engine diesel specifically for fuel economy. The previous owner claimed 10-11. I’ll know soon, but my 1500 miles seems to support his claim. I won’t declare absolutely until we get another 2K on it. And don’t forget to subtract any generator usage from your numbers.
I have one theory based on a white paper by Caterpillar (Understanding Coach / RV performance) that the fan on the rear engine RV is a part of the lower fuel economy. CAT claimed that a rear engine fan is consuming over 50 of the engine’s available hp when on at 1800 RPM. I am hoping that the constant air flow at 60 mph through the radiator of my FRED keeps my fan usage down. I don’t know if that’s real or not, but so far… we have seen10+mpg measured the correct way – averaged over multiple fills, not one trip to the pump. My car electronic meter is off by 17% – do the math and then you’ll really know what your MPG is.
I tried to find the article online to share but it’s off the CAT site. It talks about wind resistance, weight, tires – all the things which are important. Would be happy to send it to someone to post in a single location
Hi Nick. We have a 1990 TMC 102A3 converted bus with a 6V92 Detroit Diesel engine, and we get 5 – 6 mph and crawl up the steep Appalachain hills at about 15 mph.
I just computed the cost of a round trip from our home in Ann Arbor, MI to Yosemite @ 7 mpg, Yikes!
I have a 35 ft. GMC 4106 w/ an 8V71 Detroit and Allison V-730 Trans. My bus weighs about 28,000 lbs. I tow a 2001 Chrysler Mini-van, 4 wheels down. My mileage overall for the last few years is 6.5. Sounds low, but remember how much I save in Motel bills. I think most of the 10 to 12 mpg guys are dreamers.
2001 40′ Dutch Star Cummins 350
2006 CRV Toad
Usually drive about 60 MPH
7.5 — 8.1 MPG
We live full-time in a 2005 Dutch Star 40′, 370 HP Cummins. We AVERAGE getting 300 MPG ———- 7.5 on the motorhome and 600 mpg on the 2010 full size crew cab GMC that we tow behind.
We travel about 60 mph. Tried 55, too slow and did not make any difference in MPG. Drove some at 65-70 and mileage did drop 1/2 to 1 MPG.
1993 Beaver Contessa, 36 foot, 29000 lbs, 8.3L Cummins engine, 225,000 miles on same engine, 250 HP, 660 ft/lb or lb/ft which ever you prefer, of torque, tow a Jeep Liberty weighs about 4000 lbs, drive 55 to 58mph, let in roll down hills to max of 70mph, use exhaust brake when necessary, put Allison in Mode for driving, creep up hills sometimes at 25 to 35mph.
Mileage in hilly country about 8.5.mpg. Mileage on flat land 10 to 10.5 mpg.
Agree with Emery about “sweet spot” for engine. Having driven so many miles in our coach and recording all fillups/maintenance/repairs etc, our coach seems to like about 58 mph best. If we start running faster, we get lower miles per gallon.
We have an Allison 5 speed. Many of our friends have the Allison 6 speed and tell us around 62 mph is the “sweet spot” for their engine. At 55 to 60 mph the Allison 6 speed shifts back and forth between 5th and 6th gear. So we tend to run alone even when we are running with a group as each of us has different speeds we like to run and is best for our engines.
Nick, Does your Silverleaf give instand MPG?
On my gas Class-C I have a Scangauge II and by using it’s instant reading I have found my “sweet spot” and adjusted my driving accordingly. The result is my Total mpg for the first 8500 miles is 10.8 which I can document with my log.
I see highs in mid teens and lows of about 6. One thing I do is to shut off the cruse when climbing hills (as on Blue Ridge Pkwy or in PA). I find that letting cruse kick down I can see the mpg numbers drop down to 4 sometimes.
Becides What’s the hurry?
2006 40′ Allegro Bus. 8.9 Litre Cummins 400 HP Engine. Tow a Jeep Liberty 4 down. Accurate mileage and expenses kept for all of 66,149 Miles and less than 200 hours on generator. Travel around 58-62 mph. Total fuel mileage for bus is 7.77 miles per gallon. Prior to this we had a 2004 38′ Dutch Star with the 8.9 Litre Cummins 370 HP Engine and averaged 8.79 for 69,455 miles. I don’t know if the 2 foot shorter coach or the 30 hp less engine was responsible for a 1.02 better mileage or a combination of both. Towed same vehicle
2004 Coachman Sports Coach 40 foot, 330 Cat, Allison 6 speed 8 to 8.6 MPG.
At 55 MPH the transmission is not in high gear, 55 zone is when I speed up to 58 transmission up shifts then back to 56.
Using cruse control and setting 58-62 MPH will produce the best mileages, to time traveled. Longer slower acceleration, learn when the transmission will up shift, lift your foot enough to allow an up shift. Winding out each gear (accelerating in each gear until the transmission shifts, holding your foot steady) not fuel efficient.
Use the cruse control increase button one push pause one push pause to (as many as you want) slowly achieve your final set point, cursing speed. The longer pause the better and the longer time at cruse (58-62) the better fuel mileage.
Transmission – Allison; use the economy button (red light on) in the lower gears the transmission will up shift sooner. Why 58 that is about the time the transmission will shift into high gear. Lower RPM per MPH.
Lifting your foot from the accelerator before stopping (using brakes) coasting, downshifting a gear (increases drag) without your foot on the accelerator all save gas (no fuel being used) – increase miles per gallon average. Decelerating to a stoplight and not actually stopping is better.
You up shift to drive start increasing acceleration less fuel is used to return to speed resume cruse control in high gear.
Do not accelerate all the way to the top of a grade that has road signs for a steep down grade, you want to start slow going down a hill downshift a gear using brakes in a stabbing action, reducing 5 MPH then no brake , allowing them to cool.
Fuel, another thought decelerating, using the decrease button one or two pushes at a time with pauses. Does your rig have a display for “miles remaining”? If yes, when you fill note the number, this number is generated by the fullness of the tank and recent driving history. When you are driving and are exceeding previous averages the miles remaining will grow as you go down the road.
2007 Monaco Executive
Cummins ISX 525 HP, 1625 fpTorque
85836.7 total miles
13851.896 total gallons burned
$3.18 average cost per gallon
6.20 average mpg includes Aqua-Hot and 10kw genset use
7.3 average mpg per Silverleaf
Close to 50,000 pounds with Jeep Grand Cherokee in tow.
Average speed around 62-62 mph.
We have a 1982 Newell 36′ with a DD 6V92 TA (turbo aftercool) silver edition. Our GVW is around 29,500 lbs. I have a 5 speed Allison tranny. I cruise at about 58mph. We average between 7.5 and 8.5mpg depending on terrain. My friend, who drives a 1984 Bluebird, 36′ with tag axle, and same engine and transmission gets around 6mpg….he weighs over 39,000 lbs. He cruises at same speed I do. We figure the difference is partially attributable to the weight differential.
In 1984, we purchased a Chevy Wagon with the reworked 350 block diesel. We consistently got open road mileage of 29 mpg. After 40,000 miles, the injection pump checked out, so we had to have it replaced. From then on, our mileage was consistently 22 plus on the open road.
For the first 40,000 miles, when we started the car in the morning, it took about 5 minutes for it to sound like a decent engine. It rattled and banged something terrible. After the replacement injector pump was installed, it sounded normal from the start.
I was later told that the difference was in how the pump was timed. Just as with a gas engine, late timing equals less power and poorer mileage. I suspect that some of us are lucky to have a pump with the timing almost too early. The rest of us take what we get.
We have a Cat 350, 6 speed Allison, 36 foot coach and get 7.9 to 8.1
Nick, I have the same setup you have, Cummins 350, in a Sparten Chassis, 2003 41 foot Dutch Star, with 31000 miles and weighing in at 30,000 lbs. I’m lucky if I can get 7.5 at 63 MPH.
I hear folks all the time saying they get 8-10 MPG, I just wonder if there’s not just a little bit of embellishment in some cases………
40′ 2004 Dutch Star, 370 ISL Cummins (about the same engine you have), towing a 2002 Honda CRV and we now have just over 87,000 miles on the engine. We average about 7.3 to 7.5mpg each year and that has been consistent over 7 years. The highest mileage on a fill-up was 8.8, the lowest was 6.3 accounting for generator usage at 1/2 gallon an hour.
Good Morning, NICK: The advice you’ve received from posters such as Emery, above is worth its weight in liquid gold. As an old truck driver for Walmart, a portion of our pay was based upon fuel mileage. . . those of us who actually cared about being “professional drivers” consistently posted 1/2 to 1 mpg over those who simply stuck their foot in the throttle. Of course, I ran the speed limit (or a bit more) in those days where today, in the motor home I tend to run the speed limit only up to about1 or 2 mph. I keep meticulous track of my mpg in our 40′ 2010 Phaeton, and since owning it our average mpg has been 8.1 mpg. We do tend to use our generator a lot (445 hours in 10 months) so our actual milage is probably somewhat more. We now tow a 2011 Honda CR-V and have recently started using a Silverleaf ( less than a thousand miles) and our milage, according to it has been closer to 9 mpg. Time will tell. As always, oRV
Greetings from Desert Trails RV Park, Tucson,
We drive a 1967 Silver Eagle conversion with a DD 8V71 and Allison 740. We run 65-70 gov. at 72 MPH this yeilds about 6 MPG. We have been towing a Jeep Wrangler all this time and now we are shipping that back to Wichita (till it sells) and will be pulling a PT Cruiser Convertible.Bus weighs 34,000 and the Jeep about 3,400 as does the PT.
Like Orv we also run the Gen set alot. Summer travelling req. the AC to stay cool and who does not like to be cool?
We have a 2007 Itasca Horizon, 40′, Cummins 400 ISL 8.9L, Allison 300, Typical cruise control is 58 mph, 1500 RPM. We average 7.2-7.5 mpg (depending on genset use w/wo load).
117,000 miles. 450 Cummins in a 34,000 pound Foretravel. SilverLeaf says lifetime mpg is 7.5. Our sweet spot is 62 mph at around 1350 RPMs.
We have a 42′ New Horizons 5th wheel, pulled by a 1999 Volvo converted semitruck with a 400 hp/1450 torque Cummins ISM. This is the “baby” engine of over-the-road tractors. Behind the 5er we pull a Jeep Wrangler. We are about 48K lbs total. We drive at 62.
I get about 8.8-9.0 mpg overall, depending on the length of measurement. I carry 300 gallons of diesel.
Sorry to butt in on this conversation …… But, we have a 2006 Class C gasser that took us on a 6800 mile trip last summer. Average MPG was 8.1.
I have no idea where all you people that drive 58-62 MPH were during our trip because we drove 58-60 MPH almost exclusively and can only remember passing one motorhome, and never a fifth wheel. There were a heck-of-a bunch of RVs, and Semis passing us like we were standing still. The western states are especially difficult to drive below the speed limit.
We drive a 2008 Safari Passage 32′ Gasoline. Get 5 on slow coastal highways in Oregon, 9 out on the flats in Southwest Texas, and about 6.5 to 7 everywhere else. Never go over 65 due to the limitations on the CRV. 65 is our sweet spot, fuel economy drops as our speed drops. We also noticed high 7’s when we can get non-ethenol. Thinking about trading to a 2002 phaeton, hoping to get the same fuel economy. Hope that is realistic. 🙂
Hello you guys are scaring me lol I have an old 85 holiday rambler 40 limited 3208turbo cat im thinking it ways around 12,000 lb ive added an extra air hose 4 in in diamiter to the donaldson air cleaner and i think that picked it up a littel have to see its down for refurbish no computers 4 speed alison 65 on the flat no tow 10 with 20 w 40 eng oil and pefor max aditive in the eng and rear end if i dont lode it up with junk i think i can squeze11 and thats on the flat well see the air cleaners on the turbo desels are big restrictors the hose coming in is smaller than going out also muffler restrictive big inlet and outlet tomany baffels gota make it breath
We have a 2000 Winnebago real ta and get 21 MPG when not towing at 75 MPH and 14 when we tow the car.
an old holiday rambler 3208 diesel pusher 40 ft 23,000 lb not 12 thousand I wish it was 12000 LOL im reduing the mh from frount to rear every thing new big job ill be done in three mor months i bought this for the light weight every thing i looked at with out slides was heavy the mci nice but heavy the fiberglass bevers heavy i cut a lot of weight out well we see if it was worth it its a 3208T cat 250hp 4 speed alison same as a lot of the old ones aftr you take one of theas apart ther not built worth a shit just like the boats LOL lot of stapels well ther light
Had: 2001 Tiffin Allegro Bus with Cummins 330. Best mileage was 11MPG on a trip from D.C. area to Orlando. In addition to the comments above, keep the tire pressure up, keep the speed at the sweet spot (just a few mpg faster than the speed required to hit 6th gear), drive when the roads are not congested to maintain speed, and don’t carry more fuel / water/ other load than absolutely necessary. We do not tow, we bring bicycles.
Have: 2004 HR Scepter with Cummins 350 turbo diesel. Best we have reached so far is 8.3MPG, but trips have been shorter than the FL trip so far.
We have 2006 Allegro Bus with Allison 6 speed and tow Jeep Liberty. When we first got the coach it had approximately 15,000 miles on it and the average mpg on computer was 6.4. Since our purchase we have added 50,000 miles and raised the average mpg to 6.9 by driving 55-60 mph and not be as heavy footed as the original owner. I keep hoping that the computer will roll over to 7.0 soon.
Having just purchased a 1999 Allegro with the Cummins 8.3 i dont know what mileage will be but agee wth lot of comments made here.Having driven semis for couple years i am aware of progressive shifting a will sure do my best to have Allison 6 speed get in 6th speed soon an at lowest rpm possible.One thing not mentioned is it is very good idea to fill tank before shutting engine off after trip as return fuel in tank unlike gasoline engines is warm due to absorbing engine heat an if tank is not filled as air an fuel inside tank cools it will draw in outside air an moisture will condense on tank sides an as we all know that is not a good situation for a Diesel engine.
I have 25′ Sprinter based Coachman. 3.0L V 6 front diesel.
I bought it for the milage.
I can get up to 15 MPG at 65MPH Typical is 13.8-15.4 (15.4 one time only)
At 70 MPH the milage drops to somewhere between 12-13.
At 75+ forgedaboutit. 9-10 MPG.
I really like the little diesel sprinter. It’s cozy but I’ll be retiring in 5-10 years and I wanted this little bugger to last until then. For what I do, never more than 10 days at a time in it. It’s da bomb.
Full timing, maybe if you are alone.
I’ll move up to a FRED at retirement.
Question to the group: Do your diesels requiree DEF?
I have a 36′ 1991 Foretravel U300 with 6V92TA DDEC and an Allison 4 speed with a locking torque converter. I’ve gotten 10 mpg several times with the cruise control set at 60 mph. Without the cruise control I can get 9 mpg at 60 mph. I guess the computer is a more efficient driver than I am. I drove from TN to ME on one tank of diesel (1020 miles on 102 gallons) through the Appalachian mountains on I-81. I don’t get any higher mileage when I drive slower than 60 mph and of course the transmission shifts a lot more often when I travel slower than 60 mph. I normally don’t tow anything, and I normally drive with my water tanks as empty as practical, and I don’t carry a lot of cargo. I normally keep my tires inflated to about 100 psi. I check my fuel efficiency by looking into the fuel tank with a flashlight and filling it to exactly the same line inside the tank, then driving until the tank is nearly empty, then refilling to exactly that same line again.
I found this site by accident and it is without doubt very interesting !
I recently sold my 1996 Gulf Stream Sun Voyager with a Cummins 5.9 and Alison 4 speed. I have always kept good fuel records so as I can see if a problem is developing and what my costs are. I average 10.5 mpg at 56 mph. I know some say they find 55 too slow, but I have all day to get where I’m going. And the faster I go the more it costs.
But here is an interesting fact, and probably why there are so few comments in regard to the question on MPG. Doing research and asking Motorhome owners what MPG they get, 99% say they have no idea and follow through with “If you have to ask you can’t afford the Vehicle !!” Personally, If I don’t know where my money goes I may as well hang upside down in the ocean and hold my breath.
For more research I have found the Cummins 5.9 to be the most economical motor, and will again be looking for that reliable engine in my next MH.
Hope this helps…
I live in los angeles.. I bought my 38 foot american eagle in florida… 8.3 cummins 4 speed allison…
Stop and go traffic 5.5mpg
West coast of florida with lots of stop signs or signals 7.5 mpg
10 interstate to Shreveport la taking it up to 80 to see what she has. (Running like a moron) 9.5 mpg…
Shreveport to Los Angeles driving like i was trained… Running 62-65 and drafting just under 11 mpg..
Biggest thing to fuel milage
Don’t drive like a moron. And let a big rig pullyou…(drafting)