Community Forums

RonaldNC · 11-06-2010, 02:12 PM

Most of my traveling has been on back highways and roads. I've been getting around 8.75 MPG for the last several tanks.... which makes me very happy.

This last weekend, our trip was primarily driven on a major freeway... but imagine my surprise that I only got 7.6 MPG.

I'm guessing that the difference is caused by the difference of average speed. On the back highways I probably averaged 50 MPH, while on the freeway I probably averaged 60 MPH.

Based on other's experiences... am I on the right track here? or is there another explanation?

Ron

LewF · 11-06-2010, 04:23 PM

Power requirements (miles per gallon) increase roughly proportional to Velocity cubed. On our coach we sometimes average in the low 9 mpg range, towing and with the generator running, but get into the hills or have a headwind and that is down into the 7s real quick.

Lew

Pairajays · 11-06-2010, 06:30 PM

Boy, am i ever envious, 9 mpg in a 42' MH with a 425 hp engine towing a Chevy Colorado and running the generator. I squeeze out 7mpg in my 40' Marquis with a 425 Cat towing an Explorer. Of course, that's average, up hill, down hill, level and sometimes running the generator.

Jim

danes-on-tour · 11-06-2010, 06:56 PM

I have found out that my MPG varies quiet a lot. All time low = 6,3MPG. All time high = 9,8MPG. I would say that I probably average around 8MPG.

I have also discovered that a number of factors determines the result. One huge factor is how my MH is tilting when I fuel up. If it tilts away from the side I am fuelling I will get many more gallons in the tank which will show itself in my next MPG calculation. The reverse situation will obviously show up as "bad" MPG.

Another huge factor is the wind. Head wind means low fuel mileage - tail wind means high fuel mileage.

I always try to drive with a light foot on the accelerator so the way drive should not be the biggest factor, but it will make a difference if I drive in a flat landscape as opposed to crossing the Rocky Mountains.

Pairajays · 11-06-2010, 11:04 PM

The Great Dane,

I never believe the mpg on one fill up. I use the accumulated method. On a new to me MH I fill up about ten times and then use the total gallons and total miles traveled. That will give a good result. From then on I don't do any checking. You often hear that a diesel gets better milage as the miles traveled increases. I found that to be a myth. Had a new HR Endeavor that got 7.5 mpg after the first few fill ups. After 60,000 miles, still got 7.5 mpg. You want convince me otherwise.

Jim

William Willard · 11-07-2010, 10:43 AM

Jim -- I don`t know how other people get that great mpg either -- We`re on our 5th diesel pusher --93 Safari with a 250 Cummins, 96 Safari with a 300 Cat, 98 Mountainaire with a 350 Cummins, 02 Mountainaire with a 400 Cummins, & currently, a 07 42' Camelot with a 400 Cummins, & have never got the magic 9mpg -- Traveled 49 states, & all of Canada, Winter, & Summer -- If We average 7.5, we`ve had a good trip, & we tow a GMC Acadia, almost 5000 lbs. -- I have air leveling, & when fueling, I lean the coach to the oppsite side that I`m fueling, so I get a full tank each time -- The engines don`t have a flow meter, & the electronic gizmo`s aren`t accurate, so I divide the miles driven by the fuel pumped -- I`ve tried driving different speeds & techniques, & I can`t really tell much different in mph if I drive 60mph or 70 -- If I`m driving I-10 across Texas, I`m driving 70, & don`t care what fuel mileage I get -- Bill Willard

Stretch · 11-07-2010, 04:35 PM

I consider myself lucky getting 6mpg. We have a 43 ft Navigator with a 60 series 14liter engine. We also tow a 5200 lb toad. I think with all my wife's "stuff" on board we weigh out at around 50,000 lbs. I stopped by the Detroit Diesel dealer to have him check to see if a factory update had been done to the engine. He connected a laptop to the engine. Took him about 5 minutes. Within a few miles we were averaging 6.1 mpg. Nice difference. We have the Alladin System so I can see the mileage on the built in screen.

Barlow46 · 11-07-2010, 05:46 PM

Quote:

Originally Posted by Pairajays

The Great Dane,

I never believe the mpg on one fill up. I use the accumulated method. On a new to me MH I fill up about ten times and then use the total gallons and total miles traveled. That will give a good result. From then on I don't do any checking. You often hear that a diesel gets better milage as the miles traveled increases. I found that to be a myth. Had a new HR Endeavor that got 7.5 mpg after the first few fill ups. After 60,000 miles, still got 7.5 mpg. You want convince me otherwise.

Jim

Jim,
I think there are two ways to interrupt that part about a diesel getting better milage as the miles traveled increases. One has to do with a so called "break in period" after the internal metal moving parts have some time to wear and reduce friction thereby giving you a slight increase in mileage. The second way is to increase your daily "on the road" mileage. Once you get rolling on an interstate and maintain a fairly set speed for long period of time (say 3 hrs or so), you will get better mileage than if you stop at a rest stop every hour. I am not recommending that you drive for long periods of time as it can be both a health and safety hazard but it does help with the mileage. Personally, I am in favor of doing what is comfortably and I have a love for the backroads, so I will be getting less mileage but enjoying the trip more.

Dr4Film · 11-07-2010, 07:53 PM

I recently went to Alaska and back, almost 9,000 miles, and using the VMSpc, I got 6.9 mpg for the entire trip. Our coach was fully loaded, 36,000 lb's and the 26 foot trailer was fully loaded at 10,000 lb's or probably even a little more.

My coach has a Cummins ISC 350HP with an Allison MD-3000 transmission.

One thing I discovered was that it really didn't make a whole heck of lot difference whether I was carrying a full tank of fresh water or only a half to a quarter tank. Therefore, I finally got to the point where the fresh water was more important than possibly getting less than a tenth of a mpg more on the trip.

Dr4Film ----- Richard.

Denali · 11-08-2010, 11:22 AM

We have 89,014 miles on the coach. Over the life of the rig, we have averaged exactly 8.0 MPG. ISC 350, 34,000#, plus various toads, the current being 4,400#. On some tankfuls we get 6-7 MPG, on others we get 9-10, but mostly right around 8.0.

When we are in the flatlands, the largest determinant of our fuel economy is how much wind is hitting the coach. Driving the back roads at 50 MPH with no winds, we get over 9 MPG. Driving the southwest freeways at 65-70 MPH we get around 7 MPG.

BTW, I need to get up to 60 MPH before the transmission shifts into 6th. We get slightly better economy at 55 MPH in 5th.

Speed kills...fuel economy.

cj5 jeeper · 11-08-2010, 11:38 AM

I have yet to figure it out, no matter what, or how I drive I have NEVER gotten the kind of mileage other people claim to get.

danes-on-tour · 11-08-2010, 01:23 PM

Quote:

Originally Posted by Denali

BTW, I need to get up to 60 MPH before the transmission shifts into 6th. We get slightly better economy at 55 MPH in 5th.

Interesting - I need to try this out. Ours shifts into 6th at 58MPH so on 55MPH roads I always speed up to 58MPH before dropping back to 55MPH. Maybe I shouldn't?

William Willard · 11-08-2010, 01:44 PM

Quote:

Originally Posted by cj5 jeeper

I have yet to figure it out, no matter what, or how I drive I have NEVER gotten the kind of mileage other people claim to get.

I haven`t either -- Bill Willard

InPursuit · 11-08-2010, 02:35 PM

Last March I went cross country shortly after buying this rig.
But first I went from Florida up to Maryland.

Because I was new to it and to RV's in general I was a bit obsessive about speed and pace and being extra careful as I was learning my way through a whole of new stuff at once. One of these obsessions was fuel bought and miles driven notations.

On the stretch of I-20 and I-10 from Atlanta GA through San Bernadino CA...
I managed to squeeze 11.7mpg out of this 454 pushing 14,500 lbs.

Subsequent shorter interstate trips where I could keep the RPM's consistently low (2200 max) and have a minimum of stop and go I was able to get about 10mpg pretty consistently. Since then I've done a complete tune up (plugs wires cap rotor etc) but I never do better than 9mpg.

I can't make any sense out of it.