Diesel Motorhome MPG-- Honest Answers Please

[luckydog1949]

I thought it might be nice to have a place where prospective buyers could gather information that they might find helpful when shopping for a new (or new to them) motorhome.

What mileage do you get from your DIESEL motorhome? What engine do you have? What is your RV length? What is the weight of your rig? What is your normal cruising speed? Do you tow (weight of toad?) Please, keep advice on driving habits short and to the point (long theses ruin the information readability and is the same as for cars, trucks, etc.)

I'll start: We get 6.5 mpg, uphill, downhill, on the flats, towing or not. We have a CAT C7 (no DEF required - 2005). 36' long Itasca Horizon with four slides. At last weigh-in the rig weighed 29,840 lbs. We have, so far, always cruised at the posted speed limit, but not to exceed 65 mph because of our Toad's limit. Toad is a 2007 Honda CR-V 2wd which weighs about 3500 lbs.

When we had a fifth-wheel, it was hard to find believeable information of fuel "economy" for tow vehicles. And, don't get me started on the gimmicks touted to increase your mileage...

[jlandon13399]

Your MPG will depend on several factors; wind, speed of vehicle, weight of vehicle, terrain, and toad or no toad. I average 9.5 in my motorhome traveling 58 MPH. I have a H/R 40 foot with a Cummins ISB 360 HP diesel. The faster you go the less MPG.

[gbrinck]

I have a 40 foot coach which runs 37,700 lbs with car in tow, with 370 hp Cummins ISL (8.9L) engine. For years I averaged 8.0 mpg at 62-64 mph cruising on the interstates but dropped off to 7.3 in any situation where I could not run at a sustained speed. Last year my mpg fell off to about 7.3-7.7 and I'm wondering of that can be atributed to the biodiesel blends now at most diesel pumps (around 10% less energy/gallon) or some power loss in my particular engine. Will be watching closely this summer to see.

[rlbarkleyii]

My mileage for Winny, Journey 34' cummins, 275hp, Allison 2000MH, weight with Nissan Exterra toad around 29,000#. I get from 8.5 to 10.00 mpg. Tire pressure 100psi all around, 32# on toad. Best mileage on rolling hills interstate at 60-65 mph (sweet spot @ 1900rpm) on cruise control. Noticed a .50 difference between straight premium desisel and 10% bio mix.

[five]

8.4 MPG, Cummins 8.9L ISL, 400 HP, 41', 34,000 lbs, cruise at 60 MPH (MPG goes down sharply above 60), tow a CRV 3,700 lbs. Coming up on 30,000 miles and MPG has improved.

I keep a log of three versions of MPG at each fill up: MPG off the computer, straight MPG calculated from miles traveled and gallons used, and last and most accurate, MPG calculated factoring in amount of fuel used in the generator, Aqua Hot and when at an idle.

[kaypsmith]

8.3 MPG, 1988 MCI 102A3, 41.5 coach length, 6V92 Detroit ddec 3 "335" HP, cruising 70 mph, on rolling hills of Al., Ga., Fl., Tn., Ms.. 31,500 # towing Kia Soul. Gen. set has it's own fuel tank, so no need for adjustment in calculations

[wildebill308]

Welcome to the forum Lucky. A simple search should turn up more threads on mileage than you can read. This is one of the most popular subjects on the web and around the campfire. The BIG problem is there is no apples to apples comparison. Every coach is different. There are so many variables you could have two coaches that are same year same make everything but they will get different mileage. The reason is every one drives differently. I don't think you will get the same mileage if the same driver drove the two coaches on a test track.

I have a 2003 Cummins with the Allison M3000 transmission. I have changed the Muffler to a Banks muffler and added the banks Economind diesel tuner and IQ. I run in the economy mode, number 2, most of the time. Last summer towing the CR-V on a 10,000 mile trip out west I averaged 9.3 overall. I might have done better but drove 55 the whole time (30+ days) I was in California (towing speed limit) just to see if it would improve mileage, it didn’t lost 1.5mpg. My rig doesn’t shift into 6th till 65 mph so at 55 in 5th I was running 1650rpm. When in 6th I am running 1650 at 65.

Bill

[kingfr]

2015 42 ft coach, 450 Cummins, Allison 3000, 44KGVW towing Jeep Wrangler at 4K. We have gotten 7.3 MPG over its first 4,000 miles running 65-70 on Interstate and 60 - 65 on non Interstates. Should get better with age.

[desertdeals69]

I have a 32 ft which I installed a 98 ISB 275 hp with an Allison 3060. My coach weighs 19,000 and I tow a 5400 lb Silverado. When I go coast to coast 2700 miles I average 10.6 mpg. Last week I went from Tucson to Lk Havasu City, 310 miles, and with favorable conditions I got 12.4 mpg.

[hermanmullins]

"YOU WANT HONEST ANSWERS, YOU CAN'T HANDLE HONEST ANSWERS"

[sorry, I couldn't help myself.]

There are so many variables in MPG that you have to consider. In most autos people will turn off their engines when they stop for a short time but most diesel folks leave the engine running. How long does it take to build up your air pressure? Are you in the Colorado mountains or in Death Valley. Into the wind, cross wind or wind pushing you. That being said by my Trip Tec I will average 6.8 to 7.2 mpg on a trip. And when I check miles driven and fuel used I will do about the same.

Herman

[jleamont]

Lucky, welcome! We have a 40' Holiday Rambler Imperial Cummins ISL 8.9L 400hp towing a 2 door Jeep Wrangler (3800lbs). The coach weighs 34000lbs the last trip I checked it we were at 10.05mpg and the generator was running 50% of the 8 hour trip. My average speed was 58mph running the hills of I-81 from TN to PA. As stated above in my experience also the higher the speed or Bio Diesel blend will affect your mpg, not sure about you but I have never had a tail wind to help me along

[ultraglide]

We have a 2014 Winnebago Journey 42! ft we tow a tandom tow dolly with a 1200 lb Harley trike and a 06 Honda CR-V which is about 3300 lbs. we just got home from a 8919 mile trip average mileage is 7.5 mpg. Total weight of unit and tow is about 54,646 lbs.

[manholt]

Hi Lucky. I cruise at 63/64 mph, coach is 2010 Tradition, 45' with 4 slides, 2009 Cummins 425, Allison 3000...I run mostly in economy mode and put 16,000+ miles on coach last year. Toad is a Jeep Wrangler 2 door @ 3,900 pounds, coach is 60,300+/-....I get the same as Herman, 6.8 - 7.2 and I run generator when driving and Aqua Hot when I shower or do dishes. All electric coach!

That's my 2 cents, another person could get more or less...we are all different ( ).

Carl C.

[huffypuff]

I get 128 MPG descending a mountain grade, well that is what Aladdin shows me.

[alstoncorp]

We Have a 500hp ISL (Cummins) we tare out with to many clothes, too much food, then the necessary water 115 gallons ,36 gallons of propane and 200 gallons of diesel at a hefty 41680, we have a 29' trailer that is all aluminum weighing in at 2640lbs empty, then with a 5k lb Highlander in it, and extra fuel, a second Generator, Mountian Bike, and misc items, total tare weight loaded in the trailer is 7820, total rig assy 49500. We are 8k under our Max limit.

That said at 66mph we get 7.441 and at 64 we get 7.587

Running the 12.5KW genny as well we get 6.8

Running no genny and aqua hot full bore to keep it warm in the coach while traveling, we get 6.134

and a whopping 5.5 at 75mph running the genny and Aqua hot, and no car in the trailer.

we always budget our trips at 5.8mpg, so we can use and haul what we please when we please.

We keep her loaded, and keep more than required superior maintenance on her. I don't know who loves her more Blue Beacon or Cummins. Well us of course..

Neil and Stefanie..

And as far as temps, I am an old Air Cooled guy, so they are watched closely, and we have never had our tranny over 177 degrees, and the engine over 184, purrrrrs...

[manholt]

Ray. I was wondering who would react to the "downhill" part...LOL.

Neil. Welcome. Your rig is a tad ( 9 feet ) over the length limit in most States. Nice looking coach!

[smokeater75]

Hi luckydog1949,

I have a 2003 Monaco Windsor 41ft. Cummins 8.8 370hp 1200lb torque. Round trip for the last 7yrs from Winnipeg,Manitoba,Canada to Indio California cruise set at 62mph. 5000 miles round trip average 9.2 mpg. I don't tow anything and the motorhome loaded weighs in at 33800lbs. I also run synthetic oil and have my generator running 70% of the time. Hope this helps. Smokeater75

[alstoncorp]

Carl, we checked 8 states total, of 5 we have a Permit from Idaho for the Length restrictions, it did create an issue in California, so we flat tow our truck when going there. Thanks for the complements on the Coach, we take great pride and care of it.

Wish for cheap fuel prices for all coach owners to enjoy.

[manholt]

Back to mpg. I may be wrong, but I think that none off us that have large used or new DP's are all that concerned about mpg. My reason for DP is towing, air ride, comfort and space. Others have their own reasons.

Back in 08', I was camped next to a lady that had a Liberty coach 06' and she told me that her mpg was 5 on a good day, but mostly around 4.6! I guess when you pay

$ 1.3 million for a coach, mpg is not on top off wish list!

[jleamont]

Back to mpg. I may be wrong, but I think that none off us that have large used or new DP's are all that concerned about mpg. My reason for DP is towing, air ride, comfort and space. Others have their own reasons.

Back in 08', I was camped next to a lady that had a Liberty coach 06' and she told me that her mpg was 5 on a good day, but mostly around 4.6! I guess when you pay

$ 1.3 million for a coach, mpg is not on top off wish list!

Carl Agreed! When we switched from the class C to the DP last May I was curious but really did'nt care. Everyone asks me like its a big deal when I tell them 10mpg their response is always "thats horrible". I was more concerned when I am traveling that there is a place to purchase diesel fuel and if I can fit in the fuel island. It wasnt that long ago I owned a Ford F250 with a 351 and it was only getting 8mpg and you could park a few of them inside the coach, funny no one asked me then what my MPG was, that was really horrible. I am more comfortable now when we travel and with the diesel, I do not have to listen to a V10 at 6000 rpms on hills trying to build torque on a hill.

We take trips across country every other year plus the usual vacations that are in excess of 250 miles often towing a Jeep, the gasser was wound out pulling hills and I was maxed out on my pulling capacity. After those trips the Mobil one came out of the crankcase and it looked like a thin road tar, It was only a matter of time before I was going to duck a piston coming through the dog box inside . Funny thing is the V10 would average 6.0-6.5 MPG towing, factor in the price of the diesel vs gas and I am still saving money. Round trip to California I estimated I will save $400.00 to $700.00 in fuel with the additional comfort from several angles I have no complaints on the decision we made last May. Can t wait for the next trip out west!

[manholt]

jleamont. Forget the regular gas stations....go in with the truckers. Lot faster and easy enter/exit! If your in Texas, look for a big Buckees, best price on Diesel. Stay away from Love's and any Casino truck stop....the tribes don't like us much, only our $$$$.

Carl C.

[jleamont]

Carl, good advice, thanks

[deenad]

Our, new to us, Magna is 45' and weighs about 49,000#'s towing a Honda Odyssey so figure 53,000#'s or so. VMS shows 7.1 mpg for the only trip we've taken with it. That includes the Grapevine, Tehachapi and being stuck in traffic after an accident.

Stay away from the Cummins ISX 650 as it's not reliable unless rebuilt with the new parts, estimate was $29,000, but Cummins is kicking in $10,000 so we only owe $19,000 for 3,000 miles of use!

[manholt]

Deen, as Herman and I said, on the other tread. Get a new engine from Cummins...if they are "kicking in $ 10K", they are trying to get away cheap!!! Cummins have known for years that the 650 is trouble! Stand up and hold them to it...my Atty would be on them now!

Carl C.

[deenad]

Our new, to us, 2009 Magna with Cummins ISX 650 shows 7.1 mpg going from OR to AZ and almost home to WA. That's also the mileage that showed on the VMS when we did the PDI.That includes Tehachapi, the Grapevine and several hours stuck in traffic with the Odysssey in tow. Max speed is supposed to be 65 due to the Odyssey limits. That's not much worse than our much lighter Dutch Star with ISC 350 and the Magna weighs some 46,500 empty and the Ody is 4,400 at least.