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luckydog1949

Diesel Motorhome MPG-- Honest Answers Please

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My wife and I just discussed this last night, very hard to calculate MPG when you have other items pulling diesel fuel also. We ran the coach for 564 miles, boon docked at a truck stop generator was on the entire time with both roof A/C units running, once we arrived the Aqua Hot was set to "ON" for 7 days. Shut off the Aqua hot, started the generator and drove another 575 miles home, boon docked again on the way home with the generator on and both roof tops also on still. We used 134 gallons of fuel round trip, 41 hours on the generator. I ran with the cruise set at 60mph and for quite some time I had a strong head wind (fighting the steering wheel). I do not know what the Aqua hot used but looks like somewhere around 8.5 MPG plus what the aqua hot consumed for 7 days if I had to take a guess.

I did not feel like we spent too much on fuel. seemed good with us considering how large the coach is, towing 3400lbs, full tank of water and always over 1/2 tank of fuel.

After all...... it was still cheaper than a hotel, and a lot more comfortable.

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We have 2007 Winnebago 40FD diesel pusher that gets around 7.5 mpg (6.5mpg if running generator). It has the optional 400hp turbo Cummins Diesel engine. We are pulling a 1997 Toyota Camry (approx weight 3,000lb). RV has not been weighed but expect it to be around 29,000 lbs. I normally drive 65 mph. I have gotten as low as 6 mpg an as high as 10mpg (with 60mph tailwind).

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525 HP C13 in 45' Beaver Patriot Thunder flat towing Mercury hybrid. Over 20k miles coast to coast and back, and border to border we average about 48,000 lbs down the road and 25 MPG with cruise usually set to 62-63 (except in Calif where sometimes I can't get into and stay in high gear). The hybrid gets around 44 in town and coach about 6 towing or not, thus averaging about 25 mpg when some smart Alec asks. Hot head winds with Gen running may drop coach to 5.5, good consistent tail wind all day and may bump coach up to 6.2

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Although we don't have an electronic readout on mpg and other status, we do log every fill up. We have been cross country twice since we purchase our our 2000 Harney Renegade 15 years ago. It is 37' long and has 1 driver side slide. We carry all the usual accessories and more. It is powered by a Cat 3126B (330 HP) engine and an Allison 6 speed transmission. We often run the roof AC on the road, but the generator runs on propane, so it doesn't affect the mileage. If we run the dash air (and sometimes you just have to), we see a drop of up to .5 mpg.

When we first got our coach, the mpg was around 7. After about 500 miles, it was pretty steady at 8. We switched to Amsoil brand diesel engine oil, transmission fluid and gear lube at 1,000 miles just before our first cross country trip. We also installed a dual remote bypass filter, which gave us more oil capacity and better filtration. On our way east, flat towing a Honda Accord, we were behind schedule and drove at whatever the maximum posted limit allowed (and probably 5mph over that), but we still averaged 8.5 pmg. Engine temps barely increased even on long uphill climbs, and the transmission temps stayed well within the safe zone. Extremely efficient heat dissipation is a huge reason to switch to premium synthetics throughout the coach.

On our return trip, there was no schedule, so we often set the cruise to keep pace with the semi trucks. 10.5 was our best mpg going across the plains states in less than perfect weather (there were some really heavy head and side winds). 10 mpg was the norm.

We test our oil a couple of times a year to monitor its useful life as well as see what is wearing (or not wearing) in the engine. Last year when we changed oil, we used the Amsoil Series 3000, 5W30, Heavy Duty Diesel Oil.

This spring, we sold the Honda and began towing a 2001 GMC Silverado extended cab, so we could haul sporting equipment. Our mileage dropped to 8.5 - 9.5 on a two week trip to Las Vegas and the Pomona FMCA Homecoming. The mpg will hopefully be higher on our next trip, as we discovered we had owner installation errors with our EZ Brake unit and burned up the front brakes, rotors and drums on the trip.

The brake destruction issue could be a whole other thread on proper placement and installation of the pedal activation unit. Our mechanic suggested we file an insurance claim. We didn't think it applied, but State Farm Insurance actually covered the majority of the $1,400 repairs under the Comprehensive portion of our policy. The wonderful claims adjustor said it fell into the same area as having a solo accident in a parking lot (owner error).

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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.

Gary, That is a good point I didn't think of. Here in California, they seem to change the diesel fuel blend on a whim.

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We have a 2004 40 foot Winnebago Vectra.

Cummins 350 ISC.

Weighs 32,000.

3 year average MPG is 7.14

All over country so varied terrain.

Worst was about 6 MPG

Best was about 9 MPG

The MPG does not vary much from 7.14 however.

I suspect the "Worst" and "Best" above was just due to under fill/overfill at fuel up time.

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I get 8.5 on my Tiffin Allegro Bay FRED 37 ft towing a 3500 lb Saturn Vue. I run at 1950 RPM on the Cummins ISB 6.7 engine which is 62 MPH.

Previously I towed a 16,000 lb 5th wheel with a 2006 Dodge 3500 dully. I added the Banks Power Economind and went from 8-10 up to 10-12 towing @ 1900 RPM and 14-16 up to 22 running solo in the freeway at 70 MPH.

Considering adding the same to my Allegro Bay. The add on paid for its self on the Dodge Truck.

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Our coach is a Tiffin Allegro Bay FRED 34XB. 300 Cummins, In the two years we have driven 20K miles. The average is 8.9 running 65 with a toad. On one trip broke in to 11 MPG with no toad and driving 55 on the Natchez trace. :)

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I get 8.5 on my Tiffin Allegro Bay FRED 37 ft towing a 3500 lb Saturn Vue. I run at 1950 RPM on the Cummins ISB 6.7 engine which is 62 MPH.

Previously I towed a 16,000 lb 5th wheel with a 2006 Dodge 3500 dully. I added the Banks Power Economind and went from 8-10 up to 10-12 towing @ 1900 RPM and 14-16 up to 22 running solo in the freeway at 70 MPH.

Considering adding the same to my Allegro Bay. The add on paid for its self on the Dodge Truck

When we had a Winnebago Chieftain many years ago, the Banks system gave us the biggest boost in economy of anything we tried and it also helped the engine run cooler on climbs.

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The two biggest things I have found that consistently affects me are, wind and temperature. both will play havoc with your MPG. One bit of advice an "old timer", his words not mine told me years ago was watch your weight. one trick he said he uses is to not fill his water tank to capacity if he is making a trip and will be hooking up to cg water. he said he only filled his tank about a quarter full to use for coffee, cooking and the toilet only in an emergency. water weighs about 8.3 lbs per gallon so with a 90 gal tank, just filling it one fourth full will cut about 70 gals which equals around 580 lbs. this will help fuel economy but also allows for extra cargo.

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36' Triple E with a Cat 3126, toad is a 2002 Chevy Tracker. We get 10.5 mpg IF we keep the revs between 1400 and 1650. This is from 55 - 62 mph depending on the wind. Before we had the rad and air cooler cleaned, mileage was 8.5 - 9.0. Tire pressure is 100 lbs all around. This is actual mileage over the last 60,000 miles coast to coast and to the bottom of Baja.

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I always find this discussion interesting. I must say I watch the instant MPG, when it's not on cruise control, I use it about half the time. I do know that not using cruise control does improve my mileage a "little". I have a 2013 Knight 40df, 9.3L 350HP International, weighs approx 33,000lbs, I've yet to weigh it when it's loader, fuel, water, etc.

I tow a Tahoe, 5500 lbs. I just did a 5500 mile trip from panhandle Fl to St Mary Montana and back. Everything went and worked great. Loved it. Lots of mountains, I usually cruise at 62-65MPH. Tach reads 1500RPM at 65MPH, sweet spot is 1300-1400RPMs.

Mileage was ranging between fill-ups from 7+ to 8.7+, never averaged less than 7+MPG between fill ups. So far I'm very happy with the performance. I hate to say it, but when I'm not towing and AC is off, on flat country, I have gotten 10MPG on the highway, no kidding. AC seems to reduce by maybe 0.5MPG and towing the 5,500, seems to be 0.5-1MPG depending on the roads and mountains. Mostly it's about the mountains, 7 in mountains and 8+ otherwise, towing with the AC on.

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I always find this discussion interesting. I must say I watch the instant MPG, when it's not on cruise control, I use it about half the time. I do know that not using cruise control does imporve my mileage a "little". I have a 2013 Knight 40df, 9.3L 350HP International, weighs approx 33,000lbs, I've yet to weigh it when it's loader, fuel, water, etc. I tow a Tahoe, 5500 lbs. I just did a 5500 mile trip from panhandle Fl to St Mary Montana and back. Everything went and worked great. Loved it. Lots of mountaines, I usually cruise at 62-65MPH. Tach reads 1500RPM at 65MPH, sweet spot is 1300-1400RPMs. Mileage was ranging between fill-ups from 7+ to 8.7+, never averaged less than 7+MPG between fill ups. So far I'm very happy with the performance. I hate to say it, but when I'm not towing and AC is off, on flat country, I have gotten 10MPG on the highway, no kidding. AC seems to reduce by maybe 0.5MPG and towing the 5,500, seems to be 0.5-1MPG depending on the roads and mountains. Mostly it's about the mountains, 7 in mountains and 8+ otherwise, towing with the AC on.

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How do you measure fuel usage in the generator and Aqua Hot unit? I have a Tiffin Allegro Bus 45OP if that helps you.

I called Cummins, Aqua Hot and Onan and they gave me the numbers for fuel burn, here they are (all figures are gallons per hour):

8.9L ISL at idle: 600 rpm .5; at 1,000 rpm 1.0; at 1,200 rpm 1.2

8 KW Onan: no load .13; at 50% load .5; at full load 1.0

AH: .4

I did the math and subtracted the fuel burn from above from the total and computed a new mpg.

We recently changed coaches and the new AHs do not have an hour meter. The tech said they want customers to perform maintenance based on the calendar, not the hour meter.

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36' Triple E with a Cat 3126, toad is a 2002 Chevy Tracker. We get 10.5 mpg IF we keep the revs between 1400 and 1650. This is from 55 - 62 mph depending on the wind. Before we had the rad and air cooler cleaned, mileage was 8.5 - 9.0. Tire pressure is 100 lbs all around. This is actual mileage over the last 60,000 miles coast to coast and to the bottom of Baja.

I must add that our best ever was 12.2 and the worst, 8.6 mpg. Using the cruise does make a difference, especially in windy conditions. And the toad weighs in at 2400 lbs. Mountains seem to make little difference, as you loose on the climbs what you gain on the descents. We have never knowingly used bio-fuel. We do not use engine A/C when driving, rather we use the roof A/C and run the gas Onan for A/C power.

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2015 Forest River Legacy 360RB (39'), 340 hp Cummins with 2014 Jeep Wrangler Unlimited toad; all trips so far are right at 10.0 mpg and have not appeared to be impacted much by terrain and the toad. Typical cruising speed is 63 - 65 mph.

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45' 2009 Country Coach 525 Cat... Minnesota flat land ... Coach weight average load... 43,000 Best average achieved 7.5 at 60-65 freeway no trailer. Average overhaul no trailer 6.8 to 7.0

With ATC stacker trailer 8,000 lbs plus load of 10,000 pounds of car, motorcycles, golf cart and other we average about 5.2 to 5.5 on flats with avg wind. Friend with same coach and numbers heading west to West Yellowstone averaged high 4's on trip yesterday... on his return.

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There are many variables in fuel economy. I have a 45' RV with a 500hp DD and my towed vehicle is Class B Sprinter. The RV is usually loaded to 53,000+ lbs and the Sprinter weighs in at 8,000 lbs. This spring I took a 3 wk, 5000 mi round trip to Rhode Island and fuel economy varied from 6 to over 12 mpg, overall fuel economy was 7.2 mpg. This includes fuel used by the Aquahot and the 62 hours of generator use. I got 12 mpg on the leg from Albuquerque to OK City with a 40-50 mph tail wind.and lost that gain on the trip home with a 40-50 mph head wind from OKC to ABQ. Going home from ABQ is 30 mi with a 2000' elevation change and fuel economy is ~ 4 mpg. Going North from ABQ to Denver includes 1 mountain pass and I get 7 mpg without the towed and 6.5 mpg with the towed. I drive based on the brake specific fuel consumption curve, BSFC, for this engine which is flat from 1200 to 1550 rpm and above 1550 rpm fuel consumption increases, 1500-1550 rpm corresponds to 65-68 mph. The transmission is an Allison B500 that I keep in economy mode unless I lose too much speed and start obstructing the flow of traffic. I budget a fixed amount for fuel expenses and when it is spent the RV is parked. I had a Newmar DP with a Cummins 300hp C-series that averaged almost 7.5 mpg for the 70,000 miles I owned it. The next RV averaged 6.2 mpg for the 180,000 miles I put on it. The current RV has 120,000 miles on it and I am getting 6.6 mpg because I usually have my toad.

Food for thought is the RV has two alternators, one for the chassis and one for the house. The house alternator is 6.5 kW and engine fuel consumption at idle is 0.5 to 0.6 gallons per hour. The 17 kW generator is 17 kW and uses 0.8 gallons per hour. The RV has two 50 amp 120 legs or 12 kW total. Is it better to run the DD to power the alternator or the house generator?

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Just converted to 2005 class A Monaco Safari 38PDQ 4 slide, from 2007 C class Jayco Melbourne 29 3 slide. . The 6.8 V10 Ford gave me 10.5MPG Canadian, same as this 350hp Cat C7 diesel. About 8.5 mpg USA.Toad is 2011 Ford Edge for both. I run at 60mph on 4 laners and 55mph on 2 laners. I think this is quite acceptable.

I use the gallonage / mileage method. DON'T let any of those people that holiday on jets tell you about your fuel consumption. You can drive a small car for YEARS, on one passenger seats worth of aviation fuel burned. I should have switched to a DP years ago. I'll never go back !! The big horns alone, were worth it ! LOL.

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We just did a 738 mile round trip. No vehicle towed. THOR Palazzo 35.1. 1/3 tank fresh water. We managed 10.03MPG, route taken was PA TPK NE Extension/I-81. Many grades. First long run we made, am pleased with the mileage.

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We have a 2001 Itasca Horizon towing a 06 Saturn Cat engine & just had a computer check which indicated 8 mpg ave 60 mph total mileage 75,000. I don't get in stitches over the miles per gallon, just looking for comfort and is of driving over all types of terrain even up to the Grand Canyon.

Enjoy what you have and save the worry for someone else.

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Our rig:

2002 Holiday Rambler Imperial 40PST with Cummins ISL400

Weight: 34,350 lbs. Normal cruising speed 62 mph in California, 65 to 70 mph outside CA.

We tow a 2003 Jeep Liberty Limited 4wd weighing 4,200 lbs.

We bought our rig in January 2010. Since then we have driven 37,713 miles using 4,896.89 gallons for an average of 7.7 mpg.

We have traveled across the lower 48 from San Diego, CA to Houlton, ME, from Blaine, WA to Key West, FL towing our Jeep, running the generator to power the roof air conditioners at the co-pilot request.

Full Timers, with a two year stop for maintenance and parts replacement on the driver, Joe & Margie

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...There are many variables in fuel economy. I have a 45' RV with a 500hp DD ...

What make model coach do you have? Several of us here are trying to find other owners with the 500hp DD.

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We concur. We have a 2006 Itasca Horizon with a 400 Cummins and tow a 2011 CRV. Its always the same @ 6.5 to 6.7 mpg. Full timers, but we've only gone 14K miles so far. The east coast is OK but were looking forward to getting back west of the Rockies.

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