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Topic: MPG (Read 3198 times) previous topic - next topic

Re: MPG

Reply #50 –
Quote from: wolfe10 –
Quote from: ncaabbfan –
Quote from: wolfe10 –
For a better understanding of the factors affecting coach performance and MPG, this Caterpillar Corporation document makes excellent reading (and applies equally to other diesel engines):  https://ohe.cat.com/cda/files/287140/7/LEGT5364.pdf

I am not able to access the referenced article. Can others access it?

Thank you.

Yes, Caterpillar Corp has redone their website since August.

Try this one from the Caterpillar RV Engine Owners Club-- same document:
http://f1.grp.yahoofs.com/v1/ENzzTKLhVJ6YlEHx00b2bR6_cukrzTdNpjjvwR0Iihg2BwJdroJYywJCOsZk_al8crafzrXO1MyTrCIYFMT7gw/Understanding_Coach_RV_Performance.pdf

Brett Wolfe

Unfortunately, I still cannot see it....get the 404 error code, page not available.  Thank you very much for your effort.
Morris and Janice
1997 U270 36'

Re: MPG

Reply #51 –
I am surprised that no one commented on my reported 22-23 mpg on my F150. :D :-X :))
Guess I should fess up, it does get 17.33 mpg over 4 tank fills on way to Nac. Today in motel in Monroe, Ms.  so about 200 miles to Xtreme.

Re: MPG

Reply #52 –
Quote from: Dave M –
I am surprised that no one commented on my reported 22-23 mpg on my F150. :D :-X :))
Guess I should fess up, it does get 17.33 mpg over 4 tank fills on way to Nac. Today in motel in Monroe, Ms.  so about 200 miles to Xtreme. 

I thought the 22-23 mpg sounded too good.....I have a 2003 F150 with the small V8 (4.8L??) and get around 15 mpg.....but I don't have any knowledge of the V6 other than my recollection of the mileage comparison I got when we bought ours.  I didn't think there was much difference in mpg between the small V8 and the V6.
Morris and Janice
1997 U270 36'

Re: MPG

Reply #53 –
Quote from: ncaabbfan –
Unfortunately, I still cannot see it....get the 404 error code, page not available.  Thank you very much for your effort.
Try this.
The selected media item is not currently available.
The selected media item is not currently available.Barry BEAM #16014
2003 U320 40' AGDS
Beamalarm, Foretravel technical help and specifications
"Whatever the mind can conceive and believe, it can achieve"

Re: MPG

Reply #54 –
 :)  Morris, I am the most surprised about this, First the V6 is a 4.2L, 5 Speed and 3.54 rear.
I ran from Nac to Va mostly 75-80mph in a lot of rain, Not heavy, just damp/wet. did not do the math but guessed it to be about 16.5  about.
Left Va yesterday gong back to Nac, drove more 80 than 75 at this point, am in motel in Monroe, La. and filled 4 times, totaled ,did math and sure nuff 17.33, I wonder what it would be if I drove like I had a little sense?  The big thing that happened, it runs so much better, a big improvement in power, runs alike the Chevy 283 on a good day.
I was expecting about 13-15 mpg maybe ! The real dumb thing, I drove in 4th today at 80 for about 90 miles before I realized it should be in 5th, Too many years with the automatic I see.
O think I am trying to blow it up so I can justify a newer truck with cruise control

Re: MPG

Reply #55 –
I've owned several fairly late-model F-150's and guessed your tongue was firmly in your cheek on the mileage claim.
Chad & Judy
'98 U320 - Build #5315
Motorcade 16317
Wickenburg, AZ

Re: MPG

Reply #57 –
I have a 23 year old Mercedes diesel car.  In some circles, I tell of getting 38MPG on a tank-full while driving to and from work on congested Los Angeles. I leave out the tiny detail that the odometer was reading 16% high at that time.  (It was really 32MPG).

Tom Lang K6PG (originally  KC6UEC)
and Diane Lang
2003 38 U295 build 6209
2016 Jeep Grand Cherokee Summit Ecodiesel
still have tow-ready 2006 Acura MDX 
Temple City, California
Motorcade 16681 California Chapter President
SKP 16663 member of SKP Park of the Sierra, Coarsegold California
FMCA F071251
Retired electrical and electronic engineer

Re: MPG

Reply #58 –
I was a professional pilot for 35 years.  I know about drag.  Aerodynamically, we are pushing an 8'x10' barn door into the air.  My hand from wrist to fingertip is about 25 sq. inches. Hold your hand out the window  palm forward at 55 and then at 70.  Now imagine that additional force increased by times 460.  That is the additional air pressure against the front of the coach(mirrors not included)  that the engine must overcome when going  70 instead of 55.  That extra engine work is not free my friend.  It's a major fuel burn. I believe I remember from the Cummins manual that the most efficient RPM is around 1500.  If you are at a speed where 6th gear gives you 1500RPM, that should give you the best MPG.  Anything faster is additional air drag.  There is no way that 70mph will give you better milage than 55 unless you're going down hill with a tail wind.  Using the electronic incline meter in my dash to ascertain that I am on a level highway, an observing the surrounding trees, brush, or blowing plastic bags to check for wind, the dash readout on a flat hwy with no wind  at 70 is 6.3.  At 55 it increases to about 8.5.  This is with a 42' Phenix and a 525ISX engine.  If you think ambient wind isn't much of a factor, I offer the following.  Pulling a 25'  Airstream with an Escalade into a 30mph head wind going north in western MN, the instand MPG read out was 7.  With the same trailer and car, with a 30mph tail wind going east from San Diego to Yuma, the MPG read 19.  And an Airstream is much more aerodynamically efficient that a motorhome.  Both highways were level.  So the next time you get better mileage at 70 than at 55 check the winds and the incline of the highway.  Or your math.
Bob Raab
2006 Phenix 42'

Re: MPG

Reply #59 –
I, too, was a pilot in my working life.  One of the most useful features of the little black boxes with buttons we had up front was "specific fuel usage."  (Especially when trying to get back to New York or Montreal from places like Milan...)

When first owning a motorhome, I remember reading a rather large book from the Wichita Library, THE AERODYNAMICS OF LARGE VEHICLES.  It contained more information than even I wanted to know.  But I learned a couple of neat things:
    1.  The best radius of curve for the body edges was about 6 inches.  (One reason we upgraded to a FT from our older, other brand.)
    2.  The "skirt" in the back hanging near the road surface is a drag reducer.

Early in my ownership, I found that my used FT liked to go fast.  And if not using the cruise control, I found us sliding along at 75 to 80 on interstates.  Later, we usually avoided boring interstates in our travels.  My mechanical 8.3, 1996 coach likes 63 mph indicated.  (I run on oversized tires.)  The only time I was concerned about MPG was in rural Alaska where we used the generator a bunch and the fueling options had many miles between them.

Andy1
Carolyn and Lewis (Andy1) Anderson
1996 U270 36'

Re: MPG

Reply #60 –

The 'sweet spot' for my 93 U280 and my 95 U320 is 63 mph. Although I can get better mpg slower, its a great combo for making good time, excellent mileage, not being a traffic block (and inciting road rage), etc, etc. The 95 is a bit more flexible and is happy up to 65. Anything over that and the mpg drops dramatically.
I also don't feel comfortable at speeds over about 67 mph. Its the vehicle, not me. I routinely drove my v8 quattro(s) at 90-140 in years past. But then they were designed to run 155 all day long.
The selected media item is not currently available. Dave Head & Megan Westbrook
Titusville, FL - The Great Outdoors
'98 270 buying this month
Toad is a 2018 F150 XLT

Re: MPG

Reply #61 –
Andy,

Thank you for an intelligent explanation of drag and why our coaches  --  while being "made to run"  -- are not made to get better mileage at 70 and 80 MPH  vs at 55 to 65 MPH as I have read on this forum (not this current thread) in past years.  We all like to brag, but it is hard to refute physics.

Sweet spot on our coach is around 1350 RPM and between 61 and 64 MPH.  Our lifetime MPG per Silverleaf VMSpc is 7.5 over 117,000 miles.
George Stoltz.  Retired from full-time living in a great Foretravel and now are back to living in a traditional sticks and bricks in Florida.