Diesel Motorhome MPG-- Honest Answers Please

[wildebill308]

Well Lucky dog 1949 has gotten a lot of "honest" answers to his question. To bad he hasn't posted on this thread again since starting it. I believe that all of them are right and correct. Now you might ask how can this be? The answer is simple there are to many variables. I don't think 2 people driving the same make model coach on a test track can get the same mileage.

We all like Gas Mileage threads because many like to brag how well they did and some want sympathy for how bad theirs is.

One big takeaway I have is how much better engines have gotten in the last 20 years. As coaches have continued to grow in size and weight and engines continue to grow and become more sophisticated mileage has stayed about the same. I think the newer after treatment engines are getting better mileage than ever. I think it is amazing that a 50,000 lb coach can get what 5-8 or more. While the smaller /lighter coaches are getting 10+.

Now you have to account for driving conditions and driving style. That can put the mileage back in the lower ranges.

I can see how it is an important subject for the newer members who may not have as much experience driving a coach. I remember taking pictures of the first fill up over $250.00. This isn't like filling the Civic. It is nice to have the reassurance that this is normal, if scary.

Bill

[pilot92270]

On a good a good day I'm looking for 6 to 6.5. Monaco 42 (actually 43) with a DD Series 60 525hp.

[wayne77590]

Stilll on our 3-1/2 month trip but will be back home next week. From South Coast of Texas to the Left Coast up and back down half way, then and now headed home. Dash MPG reads 8.9 MPG. 2008 Cummins ISB 340 hp, 40 foot Winnebago Destination MH. On shorter trips I have had as low as 7.9 on one rip to 10.2 on another. Lots of variables.

[manholt]

Hi all.

Just returned Sunday from 4,118 miles. Avg. mpg 6.4 on a 09' Cummins 425, Allison 3000. If I use the dash computer or Silverleaf for mpg, I would be on the side of the road, looking for Coach net to bring me fuel! Constantly!

I zero my "B" trip meter each time I re fuel, then I can divide my miles by gallons=mpg. Sometimes I can run all day with no AC on, but in Summer I run my generator and all 3 AC's if needed. The computers do not compensate! I generally get an avg. of 6.1 with gen on.

I have a 150 gallon tank, but fill around 600 miles/90+/- gal. In July I took 112 gallons in Abilene, TX.& that is pushing it as my gen will shut off at a quarter tank, 37 gal. You do not want to do that in Texas, in July!

Carl

[desertdeals69]

Got home Saturday after a 21 state, 5+ month trip. Went 7389 miles and burned 735.773 gal of diesel for an average of 10.04 mpg. I have a 32 ft pusher towing a 1/2 ton Silverado. What was surprising was the "low" cost of diesel. Mid summer it had dropped to $2.33 in NH to $2.08 in Tn to $1.99 in Ok.

[cauffield]

I have a 2009 Gulfstream Tourmaster Constellation 45g with a 425 HP Cummins, towing a 4700 lb Jeep Grand Cherokee. I usually keep my speed between 64 - 68 miles per hour with the cruise control on. I usually average 7.0 to 9.0 MPG. Running the cab air and the 12.5 kw gen with one roof unit on.

The largest factor I have discovered is the Air Temperature, and the different elevations. When the air is cool and crisp she loves it. On the back side we live in Florida and the humidity and heat really destroys that HP.

Another little tip I found from truckers, is watch the alcohol content in the fuel. The more alcohol the lower your MPG. I just wonder if it is mixed for freezing or cold weather. Open to comments.

These are just my observations. I would like to get a Scan D. and see how close it is.

[bandorr2000]

Just finished an approx. 3300 mile, 11 state, 3 week trip. Was ( pleasantly ) shocked to average 9.89mpg. 2014 Thor Palazzo 35.1, 2015 Chevy Equinox LT toad.

[wildebill308]

I have a 2009 Gulfstream Tourmaster Constellation 45g with a 425 HP Cummins, towing a 4700 lb Jeep Grand Cherokee. I usually keep my speed between 64 - 68 miles per hour with the cruise control on. I usually average 7.0 to 9.0 MPG. Running the cab air and the 12.5 kw gen with one roof unit on.

The largest factor I have discovered is the Air Temperature, and the different elevations. When the air is cool and crisp she loves it. On the back side we live in Florida and the humidity and heat really destroys that HP.

Another little tip I found from truckers, is watch the alcohol content in the fuel. The more alcohol the lower your MPG. I just wonder if it is mixed for freezing or cold weather. Open to comments.

These are just my observations. I would like to get a Scan D. and see how close it is.

They don't add alcohol to diesel they add bio diesel. Yes the more bio diesel the worse the mileage.

Bill

[five]

DDEC: Detroit Diesel Electronic Control (DDEC) system.

ISL: Cummins 8.9 liter engine. 370-400 HP. Most 1,200 lb-ft torque. Can have either engine compression brake or exhaust brake.

ISB: Cummins engine. Early ones 5.9 liter. Later ones 6.7 liter. Cummins smallest engine used in motorhomes

Properly cared for, the diesel engine will outlast the coach.

FYI, the ISL is now increased to a max of 450 HP and 1,250 lb/ft torque. Those numbers are also the max for the Allison 3,000, any more HP or torque requirse the Allison 4,000.

[wolfe10]

Yes, with the new late-model emissions equipment, HP on virtually all diesel engines is up. Just as with gasoline engines when they went to catalytic converters, with all the emission equipment, the engine can run dirtier and it can be "cleaned up downstream".

[expdek570]

***Adding return trip info***

2015 Fleetwood Expedition 38K, Cummins ISB 6.7L, 360HP towing a 2013 Ford Flex. Generally run 63-64 mph on cruise control.

Charlotte NC to Greeley CO via I-40 and I-70, 1647.1 miles, 8.4 mpg overall, 195.5 gallons used. I find the dash monitor to be very, very accurate on fuel used. When I stop to fill up, I usually come within a fraction of a gallon of the monitor reading, so I feel comfortable with the numbers above.

Heading back home tomorrow, I'll post the return trip numbers when I have them.

Greeley CO to Charlotte NC via a more northerly route (I-80 across Nebraska/Iowa/Illinois then down through Indiana/Ohio/West Virginia/Virginia/North Carolina), 1743.2 miles, 8.6 mpg overall, 202.1 gallons used.

Considering how much wind there was on the way home and the multiple climb/descend cycles of I-77 through the Appalachians, I'm surprised the numbers were that good. But I'll take it!

Oh yes, I estimate my average price per gallon for diesel on this trip was about $2.48. Some higher, some lower.

[Trynforpar]

I have a 40ft 38,000lb Motorhome and I average 8mpg on with highway driving at 65mph.

[Glennon2434]

I have a 2001 Winnebago 35 with a Ford V10. I pull a 2008 four door Jeep. I can't pass skate boards on the highway and I can't a gas station at 4.89 mpg after a tuneup. 8 mpg would be wonderful.

[wildebill308]

That does sound a little low on the mileage. What speed are you cruising?

Have you weighed the coach?

What was done for the tune up by who?

Did you see if it had any codes?

Bill

[huling3]

I wish I knew what my MPG was but living in the Pacific NW we seldom see a flat spot and over the course of a couple of tanks of fuel I can only guess. We have a 2003 HR with a 315 hp cummins 38' with a toad at 5000#. The biggest problem with our fuel tank is trying to get the same level each fuel stop. Did it once and on flat run for 9.75 mpg. We use 7.5 mpg to estimate our fuel stops and I only worry about getting in and out of a station.

[five]

Several posters have listed MPG, weight of coach, speed, etc...but don't tell us the engine. Also, if Cummins, listing HP doesn't tell the full story. At times ISBs/ISCs have had the same HP and ISCs/ISLs have had the same HP.

[wildebill308]

I wish I knew what my MPG was but living in the Pacific NW we seldom see a flat spot and over the course of a couple of tanks of fuel I can only guess. We have a 2003 HR with a 315 hp cummins 38' with a toad at 5000#. The biggest problem with our fuel tank is trying to get the same level each fuel stop. Did it once and on flat run for 9.75 mpg. We use 7.5 mpg to estimate our fuel stops and I only worry about getting in and out of a station.

Easy enough to get a fairly good idea of your MPG just do an average of the last 5 fill ups. I use Gas Buddy and it keeps a running average.

Bill

[CarlAda]

I found Gas Buddy to be a great way to track mileage. This year so far, my Cat 9 on a 40 foot Country Coach pulling a Cadillac CTS averaged 7.37 mpg. Most of my travels have been up and down the Pacific NW and the western states over mountain passes and along flat stretches.

[silverado5747]

We have a 2015 Tiffin 37PA with an ISB 340 Cummins. We drove to Gaffney SC for some warranty work on frame and on the way down from Maryland we averaged 10.5mpg. After they did the 12 month service on the coach on the return trip I was surprised to see 11.3 on the fuel flow meter. Towing a 2002 Honda Accord V6 and keeping speed around 65.

[roadster27]

We have a 1999 40 ft American Tradition 40TVS with 330 hp 8.3 ISC Cummins, 6 spd 3060 Allison trans, 7500 watt quiet generator

single rear axle weighing in at 27,500 lbs, 295 x 75 x 22.5 Toyo tires.

On our trip from Detroit to Jasper National Park , 2500 miles, we got 10.8 mpg @55 mph (1475 rpm) and 10.4@60 mph (1650 rpm) and with the generator running an avg of 4 hrs a day, a couple of times got it up to 75 mph down hills , no slower than 45 mph up hills, no major mountain passes and normal cool down and warm up.

No toad and dash AC on 90% of the time, bought cheap fuel with lots of foam, took an hour to fill up at one station, 25 cents a pull. We were full of water leaving Detroit and dumped once on the trip .

I was quite happy with this as my GAS 34 ft Georgie boy gets 8.8 @ 55 at the very best across the plains (west to east downhill )

and the ride was much smoother and quieter and the 40 ft is 10,000 lbs heavier.

[fagnaml]

I stumbled on this info exchange after searching for driving speed.  After several trips from Houston to Baton Rouge I found my 2007 Damon Astoria "feels good" at ~2100 RPM and 63 mph which gives me ~ 9 MPG including crosses the big I-10 bridges over the Calcasieu and Mississippi Rivers while towing my Jeep Wrangler.  While I get passed often by all types of vehicles, including motorhomes, fifth wheels and semis, etc. 63 mph just feels right.

And no I'm not a 57 year old fuddy-duddy!

 

[BillAdams]

No worries.  I travel at the speed limit unless the speed limit is above 75.  Between FL and TN the speed limit was 70.  I set the cruise so that I stayed between 68 and 72 MPH (usually closer to 72) and had a great drive at about 5.5 MPG.  300-400 miles per day is my normal day since I travel on business.  Getting there is more important to me than smelling the flowers along the way.

[wildebill308]

2 hours ago, BillAdams said:

No worries.  I travel at the speed limit unless the speed limit is above 75.  Between FL and TN the speed limit was 70.  I set the cruise so that I stayed between 68 and 72 MPH (usually closer to 72) and had a great drive at about 5.5 MPG.  300-400 miles per day is my normal day since I travel on business.  Getting there is more important to me than smelling the flowers along the way.

That is not bad for your rig. One of these days you can join the ranks of the unemployed. I once drove from San Antonio to Washington DC non stop. Now 300 miles is a long day.

Bill

[hermanmullins]

Bill 1, I also travel with the traffic when possible. When driving at 62 to 63 mph, I might get 7.0 to 7.2 mpg. At 72 to 75 mph I will get approx. 6.8 to 6.9. I am not always in a hurry but feel like I shouldn't impede traffic by going 10 mph slower.

Bill 2, When I was on the road for my work, I to would travel 400 to 600 miles in a day. Now after 250 miles we are looking for a Wally world or park to crash. Also we have started to explore more now. When we find an interesting area, we find a RV Park and spend 2 nights. We will stay for a night, explore the area, and spend another night before starting, out fresh, to our next adventure.

Bill 1 I hope you are able to travel for leisure before too long.  

Herman

 

 

[manholt]

Herman.  Unemployment is a great institution, as long as you don't need a job!

BillA...if I had your rig, I would also feel comfy at those speeds...even for 300 a day!  Leave at 10am, shut down at 3pm!

WBill.  I too can remember doing 600-750+ miles in a day...no problem when your in your 30's, 40's, 50's...then things start slowing down, including reaction time!