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luckydog1949

Diesel Motorhome MPG-- Honest Answers Please

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Not looking a head to my 100+ gallon fill up Wednesday!  Don't think it will be any cooler in the Santos area of TX. :P

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Yes a Maxxforce 7 twin turbo.  Will be putting more miles in June on it.  I'll let you know, I'm surprised also.  Very aerodynamic styling on the coach, wheels fit very tight next to body ( not a lot of empty wheel well )  and sloped front end and that is driving at 60 mph not towing.  Also verifying using GPS distances.

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On 3/23/2015 at 6:35 PM, jlandon13399 said:

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.

Looking at a Tiffin with the isb 340. Is that engine under powered? Thanks.

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Jmholb57

I have that engine in my coach. I went from a v10 to the 340 ISB. IMO the v10 had a better 0 to 60 time but it was also in a 35 ft coach which was quite lighter then my DP. The v10 averaged around 6.5 to 7 mpg @ 65 mph. After 3 years of check engine lights with the ISB I think it’s finally running quite well. I’m not a big fan of the new clean diesels too many issues with them. One thing I’m very pleased with is my fuel mileage, 10.5 mpg @ 65 mph in a 33,000# coach. I figured this was my first DP and I wasn’t looking to go all out yet on a top of the line unit until I buy the one I retire in .When I buy my next DP I will be definitely looking for more hp.

Good luck on your purchase

Phil

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Just completed 1800 mile journey in our "new to us" 2011 Fleetwood Expedition 36M from Dayton, OH to Phoenix AZ, ISB 6.7/MH-3000 360HP/800ft-lbs (approx. 27.5K weight) averaging between 8-8.5 MPG(depending if you calculate Generator usage) cruising 65 MPH/1800 RPM.

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2005 Monaco Signature Conquest III  Cummins ISM 500HP.  We're showing 80,350 miles on the odometer and the Alladin system shows a lifetime fuel consumption of 10,128 gallons of fuel for an overall average of 7.93 MPG.  This coach approaches 48,000 lbs loaded.  That fuel economy figure sort of impresses me!  I'm the fourth owner and am looking forward to spending the summer "on the road" in this beauty....  To put it in perspective, years ago we towed a small 24' "camper" trailer behind our gas powered Dodge Ram 360 cu.in. and barely cracked the 8mpg mark with that setup!

Safe travels everyone....  TFM

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Just completed 3800 mile trip in 2004 Holiday Rambler Endeavor, 8.3 Cummins ISC, average 8.02 MPG.  Towing Dodge Dakota toad, traveling 60-65 MPH.

Jim

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Bill, you nailed it. It’s all on how it’s driven. If you just drop it in D and go you will not benefit from good MPG.

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I have a 2009 43' Holiday Rambler Scepter tag axle and I tow an Escape on a Demco tow dolly. I have an Alison 3000 trans with a Cummins 425 h/p.

I manage just about 9.5-10.0 mpg on the Scepter. I'm positive the Scepter does much better because the trans is geared differently that my Expedition was.

At 60 mph, the Cummins is turning 1300 rpm vs. just about 2000+ for our Expedition.

I traded a 2006 38' Fleetwood Expedition with a 300 h/p Caterpillar diesel. I managed 8.6 mpg towing the same configuration.

  

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2001 Safari Zanzibar with 2007 Jeep liberty toad. Have been full time June 2014 to present traveled all 49 drivable states with combined weight of 30800 lbs. Total miles driven 44,385 with average mpg of 7.9. Cat 3126b 330 hp. Mileage from Great Falls Mt. to Alaska and back dropped to 5.6 in 2014. Have had highs of 9.1 to lows as Alaska trip. This mileage is average overall for total miles driven past four years on road. 

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On 5/11/2018 at 7:48 AM, rsbilledwards said:

Late to the party but now back home after 9,000 miles of pure unadulterated freedom of being on the road since the first of January. Typical mileage towing the Chevy Tracker 3,300 pounds, rolling between 62 and 65, RPMs in the 1325 + - range, C12 425 HP CAT, Allison 4060, weight under 31,000 pounds, so 34,300 + - pounds equalled 8.5 MPG average. One 300 mile section across Texas on I 20 we saw double digits as high as 15 MPG. Add in the propane and we averaged 9.6 with the 1 gallon per 100 miles as advertised when I had it on. Some what of a guess as the frige was useing it too and for a while it used more than it should have. I filled the tank 3 times, about 100 gallons. 

 

That is amazing. The highest mileage I've ever seen or heard of in a Cat 425 is 6 MPG with 4.5 MPG being very common. 

A friend of mine used to say his Cat 425 meant 4.25 MPG! I will link him to this website so he can possibly triple his mileage. I know he will be appreciative.

 

 

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Probably would be best if you sent a PM to Bill E. His CAT has had a couple of modifications! :P

In Gillette, the Cummings Computer nerds did something with a software program, that talked to my Allison 3000.  I now climb hills with the OTR's and have got 6.39 mpg from Gillette, WY to Ruidoso, NM....We did no Interstate, all secondary roads!  With 2 door Jeep Wrangler = 60,300 pounds!  I'll take that any day.  South Dakaota via Badlands on US44, Nebraska, Kansas, Texas and New Mexico is not flat. :blink:

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30 minutes ago, manholt said:

Probably would be best if you sent a PM to Bill E. His CAT has had a couple of modifications! :P

In Gillette, the Cummings Computer nerds did something with a software program, that talked to my Allison 3000.  I now climb hills with the OTR's and have got 6.39 mpg from Gillette, WY to Ruidoso, NM....We did no Interstate, all secondary roads!  With 2 door Jeep Wrangler = 60,300 pounds!  I'll take that any day.  South Dakaota via Badlands on US44, Nebraska, Kansas, Texas and New Mexico is not flat. :blink:

Glad they were able to help with your Allison. I know you weren't to happy with it.

Bill

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Interesting this extended conversation on mileage. Driving mannerisms  can have a huge effect and the fellow getting 4.25 on a C12 mus really enjoy the power. I will say that it is a real hoot in the mountains when passed by the newer rigs on the flats and that slow considerably on the climbs to just blow by them headed up hill, no 8.5 here. .That said I know of three Safari 425 Panthers that have lifetime averages in the 8.25/75 range according to the Silverleafs. These coaches weigh in at 31,000 pounds gross and one a bit more. Two of these coaches have over 100,000 miles on them. Power is transmitted through an Allison 4000 6 speed. Sorry Carl you were shorted on this one. My coach has only 26,000 miles and is far from being broken in so runs much tighter. It still averages in the 8s with out the modification on. I drive it with the mode switch on all the time. I manually shift in the mountains and frequently pull a 24 foot Featherlite trailer loaded near 8,000 pounds from Colorado to Arizona for the winter. The Allison has had a fluid change to Transyn 295 like fluid, The differential is also synthetic filled.  As for the modification, propane injection, metered by boost vacuum is good for something a bit better than 1 mile to the gallon. One gallon of propane is good for a 100 miles give or take some. It is hard to determine here as the stove uses it as does the refrigerator so the results are some what subjective. Think about that for just a minute, 100 miles, give a bit, for for $2.75. Never the less the C12 does not disappoint or need help. It has not seen a hill it does not like. The benefits are mileage increase, (best on the flats) power increase and if abused heat increase. Boost temp gauge is highly recommended. Judicious use is recommended particularly in mountainous country the likes of Colorado and Utah  come to mind... The reason it works is that the propane causes a cleaner burn, or a more complete burn of the diesel. Another reason to have it is that it is trick and not common that works, innovation moves us forward. It is not complicated, preset and easy to install. The system I am using has been around since 2000 currently undergoing testing with the U.S.Air Force and Army for fuel economy uses.

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