24 replies to this topic

[tylercg]

My 2005 Vectra 400 Cummins get only 6.7MPG. No matter what speed (within reason), weight, towing or not my milage stays at 6.7MPG. I think that is way too low. I took it to Freightliner and the RV dealer and they say this is normal but as I meet other RV owner with about the same size RV and same type/size engine they tell me they get 8+ MPG. Others have told me it will get better after break in - but I have 18,000 miles and it isn't getting better. Even one MPG better is a significant savings - any help?

[wolfe10]

My 2005 Vectra 400 Cummings get only 6.7MPG. No matter what speed (within reason), weight, towing or not my mileage stays at 6.7MPG. I think that is way too low. I took it to Freightliner and the RV dealer and they say this is normal but as I meet other RV owner with about the same size RV and same type/size engine they tell me they get 8+ MPG. Others have told me it will get better after break in - but I have 18,000 miles and it isn't getting better. Even one MPG better is a significant savings - any help?

Welcome to the FMCA Forum.

I would agree, your mileage is at the low end.

But, the more details you give, the better we can address your issues:

What does your coach weigh?
What are you towing?
How fast do you drive?
Do you drive in regular or economy mode (Allison transmission)?
Flat land, hills or mountains?
Did you subtract for fuel used by the generator?
Is this a calculation of miles driven divided by gallons of fuel or is this from your computer?

Brett Wolfe

[bear0033]

We have a 2008 Monoco Knight 40 ft with a Cummins IS 360 engine. Initially I was getting about 7 MPG and am now in the 8.5 to 9 range. I make sure my tires are properly inflated, only drive at 60 MPH maximum, use the speed control whenever possible, had an after market air filter installed, and try my best to keep the coach weight down by keeping the water, gray and black tanks to a minimum. Also re-check your storage for unused items, we all seem to collect stuff that we really do not use. We tow a Honda CRV. I have noted that head wind and rain have a large negative impact on fuel economy, as well as mountains - big time. We have done one trip to the Rockies and one to Florida from upstate New Youk, and we have about 18,000 miles on the coach. Once, leaving NM I got 10 MPH and was really impressed until I realized I was going down hill with a tail wind.

[bear0033]

I forgot to add to the previous response that we had a two speed fan clutch installed to our ISC by Cummins to replace the big fan that was running full speed. Jon and Carolyn Cook

[deenad]

I forgot to add to the previous response that we had a two speed fan clutch installed to our ISC by Cummins to replace the big fan that was running full speed. Jon and Carolyn Cook

That's one change I'd like to make to our MH. What did it cost?

[tzimmermn]

We have a 2007 Winnebago Tour 40FD (4 slides) with 400 HP Cummins ISL engine with 25,000 miles on unit. We get about 7.5mpg on average @ 65mph on Interstate driving with full load of water and propane. We got 10 mpg once with a 60 mph tailwind from Amarillo, TX to Albuquerque, NM.

This is my experience only over the last 15,000 miles since owning coach. Brett Wolfe is right on regarding all things that can affect mileage.


Terry

[desertdeals69]

Check the accuracy of the speedometer and odometer. That is done in the engine computer. Make sure the right info is entered such as tire revs per mile. Some coaches I've traveled with claim higher mileage than I was getting yet when we fueled up we both took the same gallons. The distance traveled on the odometer was greater on the other coach even though we went the same miles.

[DickandLois]

Terry, Drop about half of the water, we travel with only 1/4 to 1/3rd. of a tank of water when traveling. Also keep the holding tanks empty when possible.
Diesels need about 50k miles on them to get broken in from my experience.
The sweet spot on mine is 62mph. regarding torque to horse power. Your engine and transmission set up is entirely different then mine so the sweet spot will be a little different.

Rich.

[TBUTLER]

It has been over three years since this discussion but this topic on Improving Fuel Mileage is still relevant. My original post and subsequent discussion have many suggestions for things you can do to improve fuel mileage. One of my primary contentions is that a major factor in determining the MPG you get from your rig is how you drive the rig. I have 106,865 miles on our rig and fuel consumption of slightly less than 12,900 gallons which works out to 8.3 MPG. I have not adjusted the fuel use for generator use. We currently have 1352 hours on our generator which would increase the MPG perhaps a few tenths of MPG if adjusted for generator use. We tow a 6000 pound Chevrolet Trailblazer almost all of the time. I would estimate that the motor home has been driven less than 2% of that mileage without the toad attached.

There certainly are physical matters that affect fuel mileage but how you drive your vehicle can significantly affect your fuel mileage.

[Allegiance40x]

I have found the two things that most affect MPG are speed and head wind.

[lforrester]

I have a Winnebago Tour, 40 ft, with 400 hp Cummins 400 and average 7.979 mpg towing a Honda CRV.

[hermanmullins]

When our coach get 7.0 mpg I feel I am doing fairly well. Last month I had to carry about 1,000 lbs of wood and a full tank of water when we went to Shawnee, OK to the Six-State Rally. Not too far just a little under 200 miles. I was getting, per the computer, 5.4 mpg.. Coming home with a very low water tank and no wood, I was getting 7.1 mpg. Now I know that size, no that's not right, weight does matter.

And while I am on the subject of the Six-State Rally in Shawnee, please keep the families and friends of the couple from Ft Worth, TX that lost their lives in the terrible accident on their way home in your prayers.

Herman

[WILDEBILL308]

Herman,

I haven't heard any follow up on what happened in that crash. Any news? I really didn't hear a lot about the 6 State Rally.

I was there but haven't seen any or limited post in reference to it. 500 Class A motorhomes get together and no one is commenting. What happens at 6 State stays at 6 States.

Bill

[hermanmullins]

FYI Bill and everyone out there.
The tragic accident happened on Saturday, September 29. Three coaches had left the Rally and were traveling together back to Texas. The first three coaches lost sight of their friends and pulled over to wait for them. If I understand it they were all out standing behind the last coach when a car or truck stopped and asked if they were waiting on another coach. they said yes and the driver told them that there had been an accident back up the road where a truck collided with a motor home and there was an explosion and every one was killed. The people in the coach plus the driver of the truck and her 4 year old daughter. As I have said it was a tragic accident.

It was a very sad ending to a wonderful Rally. We had 528 coaches in Shawnee, Oklahoma at the Heart of Oklahoma Expo Center.

Everyone make your calendar for next year, South Central Area will have their Six-State Rally September 11-12-13-14, 2013, at the Missouri State Fair Grounds in Sedalia, MO.

Herman

[trutone]

Are you checking the MPG at the Freightliner Driver Info Display on the dash? If so, that MPG readout is the average MPG for the life of the vehicle. It cannot be reset by owners. I don't know where they start at (MPG-wise), but they improve as the years go by.I've heard it takes about 150,000 miles to be somewhat accurate. I wish the readout was resettable. My Horizon 40 ISL400 (sister to a Vectra) gets about 8.5-9.25 in real world driving. I drive pretty conservatively.

[desertdeals69]

If you use a Road Relay 4 or 5 you can reset the trip mpg each time you fill up.

[hermanmullins]

trutone,

Welcome to the Forum.

You are correct about the unit giving Average MPG. I have a TripTec on our Dynasty. I just use it as a guide for the trips we take. It does have a setting that give life time averages that, as you said, can't be reset. However according to it my life time average bounces between 45.8 and 96.7 MPG.

I think I need have it checked out, do you think?

Herman

[WILDEBILL308]

Just a follow up on what some say about driving at 60 mph. I have found that my unit won’t shift into 6th till I hit 62 0r 63 mph. Just make sure you are going fast enough to be in top gear. I am going on a trip to Colorado in a couple of months so I will see what I get on reasonably flat roads heading up there. I got 8.5 towing a Honda Civic on a tow dolly before.

Bill

Herman, what kind of fuel additive are you using.....

[desertdeals69]

Usually the best fuel mileage is between 58/61. You want your transmission to be in 6th gear, if it won't, that can be set in the computer. Mine shifts into 6th at 57mph.

[hermanmullins]

Bill, I use Lucas when I do add conditioner which is about every third or forth tank full.
By the way Bill when are you going to join us, Lone Star Chapter, at a Rally?

Herman