Title: MPG
Post by: George Stoltz on July 20, 2010, 12:50:07 am
Post by: George Stoltz on July 20, 2010, 12:50:07 am
Quote from: Virginia, Jim And Cricket
/snip/
I've learned so many of her idiosyncrasies as well as her preferred cruising speed of 74mph, much more than mine, but I respect it and she and I will have a talk, but I'm afraid she will win on this one - I'll catch up :))
Virginia:
I'm not sure what you mean by preferred cruising speed. Many of the Cummins 400 and 450 HP will give you optimum performance at 62 MPH at about 1350 RPMs.
Title: Re: Re: MPG
Post by: John S on July 20, 2010, 06:41:27 am
Post by: John S on July 20, 2010, 06:41:27 am
George, in talking with FT over the years they designed our cinches to run at 70 mph. That is what they use crossing Texas and many wide open spots. The fuel milage as calculated on my silver leaf is not much different either though there is a noticeable drop a 75.
As to dealers and the best, we only have one choice but when they were all working MOT was hands down the best. I have purchased on coach from MOT and one at the factory but that is before dealers. I got great service at the factory the first time and wonderful service at MOT and by the same people. It is funny how they move between the two shops.
As to dealers and the best, we only have one choice but when they were all working MOT was hands down the best. I have purchased on coach from MOT and one at the factory but that is before dealers. I got great service at the factory the first time and wonderful service at MOT and by the same people. It is funny how they move between the two shops.
Title: Re: Re: MPG
Post by: Barry Beam on July 20, 2010, 09:59:33 am
Post by: Barry Beam on July 20, 2010, 09:59:33 am
Quote
In talking with FT over the years they designed our coaches to run at 70 mph. That is what they use crossing Texas and many wide open spots. The fuel mileage as calculated on my silver leaf is not much different either though there is a noticeable drop a 75.
John,
I found the higher speed to be optimal also.
For us non Texanss, is there any adjustments that can be made to get it optimized for the speed limit in all the other states :D
Thru software maybe on the electronic engine?
Title: Re: Re: MPG
Post by: Paul Smith on July 20, 2010, 10:19:13 am
Post by: Paul Smith on July 20, 2010, 10:19:13 am
I typically get 8.5mpg at 61mph (6th gear) and 11-12mpg at 55mph (5th gear) in rolling hills. 40ft 1999 U320 towing Honda element
best, paul
best, paul
Quote
For us non Texans, is there any adjustments that can be made to get it optimized for the speed limit in all the other states :D
Title: Re: Re: MPG
Post by: Dave M (RIP) on July 20, 2010, 05:00:30 pm
Post by: Dave M (RIP) on July 20, 2010, 05:00:30 pm
I am with the 70mph gang, I just returned from a 2498 mile "Joy Ride" , ran mostly 70ish maybe more and a lot in the 65 area, ran hard back through Ky, WV and Va mountains. The VMSpc gave 8.7 average for the entire 2498 miles.
One big reason I love the ISM450, It goes and it will not kill you on fuel burn.
As mentioned earlier, the VMSpc is very accurate on the fuel vs mileage numbers, they did a great job doing the math in that little box.
Dave
One big reason I love the ISM450, It goes and it will not kill you on fuel burn.
As mentioned earlier, the VMSpc is very accurate on the fuel vs mileage numbers, they did a great job doing the math in that little box.
Dave
Title: Re: Re: MPG
Post by: John S on July 20, 2010, 07:27:05 pm
Post by: John S on July 20, 2010, 07:27:05 pm
I typically get 8.5mpg at 61mph (6th gear) and 11-12mpg at 55mph (5th gear) in rolling hills. 40ft 1999 U320 towing Honda element
best, paul
Ok, unless you have an old GV with a mechanical engine you are not going to get the 11-12 with any 450 ISM on my coach unless I am rolling down hill. The Silverleaf is extremely accurate as Dave said and the only way I get higher than 8 or so is down hill. I have put on 300k miles on three different FT and the best I got was 9 mpg on my 34 foot U270. You have a U 320 in a 99 vintage so you should be able to hook up silverleaf and you can see your overall milage for your coach since new. I would say that it will be around 8 mpg if you are 40 foot. It is silly to discuss fuel milage when se get such high numbers but fuel is one of my biggest expenses running the coach too so I do pay attention to my coach and my throttle. Heck pulling out of a rest stop on I 81 I was getting about 1 mpg for more than 3 miles up hill.
Title: Re: Re: MPG
Post by: George Stoltz on July 20, 2010, 07:39:11 pm
Post by: George Stoltz on July 20, 2010, 07:39:11 pm
I stand corrected. I will try the 65 to 75 speeds and see if we get better mileage. Right now we are pretty much averaging 7.5 MPG.
With VMSpc you can get the lifetime miles and the lifetime MPG. Our is exactly 7.5 MPG with 110,000 miles racked up so far. Previous owner was a Texan. He must have driven like we do.
M11 450 engine.
With VMSpc you can get the lifetime miles and the lifetime MPG. Our is exactly 7.5 MPG with 110,000 miles racked up so far. Previous owner was a Texan. He must have driven like we do.
M11 450 engine.
Title: Re: Re: MPG
Post by: Barry Beam on July 20, 2010, 08:22:58 pm
Post by: Barry Beam on July 20, 2010, 08:22:58 pm
Quote
With VMSpc you can get the lifetime miles and the lifetime MPG. Our is exactly 7.5 MPG with 110,000 miles
Thats more like what I see for lifetime of coach on mine.
I was beginning to think I was behind the curve.
I can get better on some runs but it always seems to average out about that.
Although the more I drive it the better the mpg average trip is getting.
Title: Re: Re: MPG
Post by: John S on July 20, 2010, 08:25:39 pm
Post by: John S on July 20, 2010, 08:25:39 pm
Barry, I am about 6.9 mpg on mine but I did not own it for most of the miles, only a third of them. I moved it from 6.8 to 6.9 but run consistently in the mid 7s for my trips.
Title: Re: Re: MPG
Post by: Virginia on July 20, 2010, 08:49:16 pm
Post by: Virginia on July 20, 2010, 08:49:16 pm
At this time personally don't feel I need to be concerned of our '99 U320 fuel mpg rating but rather exercising her and opening her up -
We all got our coaches for our personal comfort/pleasure if we are going to belabor the MPG to me it takes a lot of the joy out of it all - ever so often I will check it out but don't dwell on it - No we do not have unlimited funds, we just plan and being full time we don't have to be paying huge electric bills and we can go a long way on what we use to pay for just electric for a house -
George to give you my opinion of your question regarding my coaches "cruising speed" she has about 96K miles on her, she was driven at higher speeds than I normally drive but I have learned over the years an engine will develop what my first husband called "cruise speed" he was an avid car "nut" - the engine will seek it's level and it just depends on how it was broke in etc - Now I know there will be lots of ya who have a different opinion that is fine and respected but this is my opinion - This gal levels out and purrs like a kitten around 69 to 74, she just smooths out and levels down into a comfortable ride - IMHO she has had lots of long highway miles which is a good thing - I've got a good one IMHO and we're going to enjoy her :)
We all got our coaches for our personal comfort/pleasure if we are going to belabor the MPG to me it takes a lot of the joy out of it all - ever so often I will check it out but don't dwell on it - No we do not have unlimited funds, we just plan and being full time we don't have to be paying huge electric bills and we can go a long way on what we use to pay for just electric for a house -
George to give you my opinion of your question regarding my coaches "cruising speed" she has about 96K miles on her, she was driven at higher speeds than I normally drive but I have learned over the years an engine will develop what my first husband called "cruise speed" he was an avid car "nut" - the engine will seek it's level and it just depends on how it was broke in etc - Now I know there will be lots of ya who have a different opinion that is fine and respected but this is my opinion - This gal levels out and purrs like a kitten around 69 to 74, she just smooths out and levels down into a comfortable ride - IMHO she has had lots of long highway miles which is a good thing - I've got a good one IMHO and we're going to enjoy her :)
Title: Re: Re: MPG
Post by: Dave M (RIP) on July 20, 2010, 09:13:12 pm
Post by: Dave M (RIP) on July 20, 2010, 09:13:12 pm
Just for giggles ;D For my last trip, I was not towing, and have the lighter 36' 320, and it does run freely, I have gotten it up to the short average of 10 mpg, that is no fun driving like that. My coach is right at 30,000 lbs on platform scale about 3/4 fuel and water,waste tanks at -0-.
Like most, the fuel game is just a game we each play. I doubt if it makes any difference to most of us. If it gets 5 or 15 mpg, it does not change the miles I drive it.
Dave
Like most, the fuel game is just a game we each play. I doubt if it makes any difference to most of us. If it gets 5 or 15 mpg, it does not change the miles I drive it.
Dave
Title: Re: Re: MPG
Post by: George Stoltz on July 20, 2010, 10:02:16 pm
Post by: George Stoltz on July 20, 2010, 10:02:16 pm
Dave,
Amen
Amen
Title: Re: Re: MPG
Post by: George Stoltz on July 20, 2010, 10:14:55 pm
Post by: George Stoltz on July 20, 2010, 10:14:55 pm
Virginia,
Points well taken. Enjoy your coach. That is what it is all about. Sandy and I often say about MPG: "it is what it is." If we really wanted to make MPG the centerpiece of retirement we would have bought a Volkswagon Vanagon. We do like the 62 to 63 MPH slot. We feel good doing that and our coach seems to operate well. But, just for fun and to play the MPG game, I will try the 65 to 70 MPH range, keeping in mind that in some states we can only drive 55MPH.
Points well taken. Enjoy your coach. That is what it is all about. Sandy and I often say about MPG: "it is what it is." If we really wanted to make MPG the centerpiece of retirement we would have bought a Volkswagon Vanagon. We do like the 62 to 63 MPH slot. We feel good doing that and our coach seems to operate well. But, just for fun and to play the MPG game, I will try the 65 to 70 MPH range, keeping in mind that in some states we can only drive 55MPH.
Title: Re: MPG
Post by: George Hatfield on July 21, 2010, 12:10:20 am
Post by: George Hatfield on July 21, 2010, 12:10:20 am
George.... check your CRV manual. Ours (2009) says the tow speed is limited to 65.
George (the other one)
George (the other one)
Title: Re: MPG
Post by: George Stoltz on July 21, 2010, 12:45:25 am
Post by: George Stoltz on July 21, 2010, 12:45:25 am
Thank you, Other George. There probably have been a few instances where we drove slightly over 65 MPH, but only for a few minutes at most. On reflection and in light of the speed restriction of the Honda CR-V, I see no reason to drive a little faster to see if we get better MPG. And there is the issue of many states not permitting us to drive faster than 55 MPH. Can't see any reason to pay speeding fines or damage the transmission in our CR-V.
Once again, I've learned something valuable that will keep us from making an expensive mistake.
Once again, I've learned something valuable that will keep us from making an expensive mistake.
Title: Re: MPG
Post by: George Hatfield on July 21, 2010, 12:58:43 am
Post by: George Hatfield on July 21, 2010, 12:58:43 am
Since we left Las Cruces near the end of April we have traveled through NM, AZ, NV, CA, OR and WA for a total of 2803 miles and a mileage (as determined by Silverleaf) of 8.2 mpg. During our trip we have traveled through some mountainous areas which, of course, has affected our mileage. The best mileage was from Tucson to Phoenix which was just under 10mpg, but of course, one looses about 1000 feet in that relatively short trip. The worst mileage was from Phoenix to Payson, AZ... 6mpg and a gain of several thousand feet in about 100 miles. We have towed a Honda CRV for the entire trip.
I'm interested in the speed vs mpg relationship. I remember reading some Cummins material from Barry's website which, if I recall correctly, indicated that the faster one goes within the cruising speed range (say 55 to 75), the lower the mpg. This is not surprising since the aerodynamic resistance goes up with the square of the velocity. There is a good discussion on Wiki about all of this....Google physics speed vs fuel economy if you are interested. Also this article from Consumers reports gives data for a number of automobiles all of which showed decreased mileage with increased speed (http://blogs.consumerreports.org/cars/2009/09/tested-speed-vs-fuel-economy.html (http://blogs.consumerreports.org/cars/2009/09/tested-speed-vs-fuel-economy.html)).
So how could FT design our coaches to get better mileage at 70 than 55? We don't exactly have an aerodynamic shape. Also, I would think that the Cummins engines and Allison transmissions would be rather standard (i.e., they are not modified nor custom built for FT). Are there any data to show which speed is best?
We normally run about 58mph. It seems like a comfortable speed to us and it is just above the shift point from fifth to sixth gear in economy mode. By the way, I have not noticed much difference between economy and regular mode as far as mileage goes.
George (the other one)
I'm interested in the speed vs mpg relationship. I remember reading some Cummins material from Barry's website which, if I recall correctly, indicated that the faster one goes within the cruising speed range (say 55 to 75), the lower the mpg. This is not surprising since the aerodynamic resistance goes up with the square of the velocity. There is a good discussion on Wiki about all of this....Google physics speed vs fuel economy if you are interested. Also this article from Consumers reports gives data for a number of automobiles all of which showed decreased mileage with increased speed (http://blogs.consumerreports.org/cars/2009/09/tested-speed-vs-fuel-economy.html (http://blogs.consumerreports.org/cars/2009/09/tested-speed-vs-fuel-economy.html)).
So how could FT design our coaches to get better mileage at 70 than 55? We don't exactly have an aerodynamic shape. Also, I would think that the Cummins engines and Allison transmissions would be rather standard (i.e., they are not modified nor custom built for FT). Are there any data to show which speed is best?
We normally run about 58mph. It seems like a comfortable speed to us and it is just above the shift point from fifth to sixth gear in economy mode. By the way, I have not noticed much difference between economy and regular mode as far as mileage goes.
George (the other one)
Title: Re: Re: MPG
Post by: George Stoltz on July 21, 2010, 01:05:07 am
Post by: George Stoltz on July 21, 2010, 01:05:07 am
snip from George Hatfield
"So how could FT design our coaches to get better mileage at 70 than 55? We don't exactly have an aerodynamic shape. Also, I would think that the Cummins engines and Allison transmissions would be rather standard (i.e., they are not modified nor custom built for FT)."
Could it be what some guys tell their wives to justify driving at faster speeds?
"So how could FT design our coaches to get better mileage at 70 than 55? We don't exactly have an aerodynamic shape. Also, I would think that the Cummins engines and Allison transmissions would be rather standard (i.e., they are not modified nor custom built for FT)."
Could it be what some guys tell their wives to justify driving at faster speeds?
Title: Re: MPG
Post by: John S on July 21, 2010, 06:56:20 am
Post by: John S on July 21, 2010, 06:56:20 am
First of all, I do not really care about milage since I usually put in more fuel than the Silverleaf says. The reason is in the summer when I do most of my travels it is hot and when I pull the coach out of the garage the first thing I do is turn on the genny. That sucks fuel and I use the diesel part of the aquahot in the winter so that takes fuel but you can guess how much by how long I have been running and if I spent the night on the road and ran the genset all night. It is a break even paying for fuel now and the campground fees but the ease of getting in and out is the reason now.
As to better fuel milage, that happens for me up to 70. I would not go so far as to say better but the same and I am on the road less so the genset is running less so I put in less fuel. I do not see a downward movement in fuel consumption till I break 75 mph. I have not really noticed any difference towing or not towing with this unit. With my 34 foot it cost me about .5 mile per gallon.
As to better fuel milage, that happens for me up to 70. I would not go so far as to say better but the same and I am on the road less so the genset is running less so I put in less fuel. I do not see a downward movement in fuel consumption till I break 75 mph. I have not really noticed any difference towing or not towing with this unit. With my 34 foot it cost me about .5 mile per gallon.
Title: Re: MPG
Post by: Bill Chaplin on July 21, 2010, 07:09:30 am
Post by: Bill Chaplin on July 21, 2010, 07:09:30 am
I think I will use 70MPH on next leg also !
Gallons Miles MPG Speed
85.83 713 8.31 60 MPH
92.424 844.7 9.14 60 MPH
74.933 535.0 7.14 60 MPH
92.164 696.0 7.55 60 MPH
81.380 666.2 8.19 60 MPH
88.604 743.5 8.39 60 MPH
69.3 512.4 7.39 60 MPH
94.6 633.7 6.70 60 MPH
100.0 832.4 8.32 60 MPH
14.4 140.3 9.72 60 MPH
95.2 756.5 7.95 60 MPH
21.3 225.4 10.57 70MPH
I needed to get home ASAP on last leg
RPM @ 60 =1625
RPM @ 70 =1900
Sweet spot ???????
Gallons Miles MPG Speed
85.83 713 8.31 60 MPH
92.424 844.7 9.14 60 MPH
74.933 535.0 7.14 60 MPH
92.164 696.0 7.55 60 MPH
81.380 666.2 8.19 60 MPH
88.604 743.5 8.39 60 MPH
69.3 512.4 7.39 60 MPH
94.6 633.7 6.70 60 MPH
100.0 832.4 8.32 60 MPH
14.4 140.3 9.72 60 MPH
95.2 756.5 7.95 60 MPH
21.3 225.4 10.57 70MPH
I needed to get home ASAP on last leg
RPM @ 60 =1625
RPM @ 70 =1900
Sweet spot ???????
Title: Re: MPG
Post by: George Stoltz on July 21, 2010, 01:45:52 pm
Post by: George Stoltz on July 21, 2010, 01:45:52 pm
We are all sure beating this topic to death, me included. I thought the Silverleaf and/or the VMSpc only took into account the fuel used by the diesel engine and not the generator or Aqua-Hot.
Title: Re: MPG
Post by: Gerry Vicha on July 21, 2010, 02:08:43 pm
Post by: Gerry Vicha on July 21, 2010, 02:08:43 pm
I have the 1994 version of the Detroit 6V92 350 H.P. - after a 10,000 mile trip the best mileage I have seen was 7.0 running on flat land. If I would average MPG it would be just under 6 . Sure wish my coach would do better. Total coach mileage is 44,500 do you think mileage will improve with use/run time ????
Title: Re: MPG
Post by: Barry Beam on July 21, 2010, 02:14:47 pm
Post by: Barry Beam on July 21, 2010, 02:14:47 pm
Quote
I thought the Silverleaf and/or the VMSpc only took into account the fuel used by the diesel engine and not the generator or Aqua-Hot.
That is correct.
I usually record the genset hours on my receipt along with the other info ie: miles etc and factor that into my calculations on a spreadsheet. Just for learning purposes which is what this thread is about.
Learning more about the performance of our coaches in relationship to others to see if maybe we need to look at something further if it seems to far off.
I rely on the VMSpc for "miles left to go" when calculating when I need to look for a Truck stop.
I set the tank gallons at 75%.
So when it says "0" miles I have 25% left to go.
Now if I used the Genset a lot I dont have 25% left to go , so it can be misleading.
I am also looking at the fuel gauge to see if they are saying the same thing.
Fortunately I usually fill up long before it gets to that point.
I only ran out of fuel once and as luck would have it, I was just pulling into the truck stop and was perfectly in front of the pump.
I don't know who was looking after me but I was sure glad.
I forgot about how much I was using the the Genset and got lulled into a false sense of security.
Trying to make it out of Calif to get that cheap Diesel in AZ ;D
The fuel gauge was correct & I did'nt listen because I was relying on the VMSpc.
Well at least I got the number I always wanted to know.
On my 180 gallon tank it only uses 160.68 gallons.
Thats my story and I am sticking to it. ::)
Title: Re: MPG
Post by: George Stoltz on July 21, 2010, 07:58:11 pm
Post by: George Stoltz on July 21, 2010, 07:58:11 pm
Yeah! Me again. We drove almost 84 miles today. We decided to stick with our 62-63 MPH range. Sandy likes 63 MPH. She is the lead footed family member. Anyway with absolutely no change in driving habits we received our highest MPG ever. We got 8.3 MPG for the trip. So I am learning what so many of you more seasoned big rig drivers already know: that there are some variables in the MPG equation that are beyond our control
Title: Re: MPG
Post by: Tim Fiedler on July 21, 2010, 08:44:21 pm
Post by: Tim Fiedler on July 21, 2010, 08:44:21 pm
MPG - I believe that the best fuel economy in a Diesel is obtained at the RPM where Maximum torque is achieved - generally a relatively low RPM in a diesel (per the cummins web site the 07 ISM450 makes peak torque at 1200 RPM), so theoretically 6th gear an 1200 RPM should yield best mileage, if only engine effeciency was a consideration. (I am not a mechanic, and may be way off here, please, just flame me gently) :-)
For a whole bunch of interesting information on MPG (much geared to OTR drivers of Semi's, but much useable for our FT's) go to this link
http://www.everytime.cummins.com/every/misc/mpg.page? (http://www.everytime.cummins.com/every/misc/mpg.page?)
Then click on the words "Check out Dr. Diesel's Secrets to Great MPG" which are in red text.
Here is the Cliff notes from the 37 pages: Enjoy -
Tim Fiedler
Rock-Solid Rules
Every 2% reduction in aerodynamic drag results in approximately 1% improvement in fuel economy.
Above 55 mph, each 1 mph increase in vehicle speed decreases fuel economy by 0.1 MPG.
Worn tires provide up to 7% better fuel economy than new tires.
Used lug drive tires can get up to 0.4 MPG better fuel economy than new lug tires.
Ribbed tires on the drive axles provide 2% better fuel economy than lugged tires.
Every 10 psi that a truck's tires are underinflated reduces fuel economy by 1%.
The break-in period for tires is between 35,000 and 50,000 miles.
Tires make biggest difference in MPG below 50 mph; aerodynamics is the most important factor over 50 mph.
The most efficient drivers get about 30% better fuel economy than the least efficient drivers.
Idle time is costly. Every hour of idle time in a long-haul operation can decrease fuel economy by 1% because you're burning fuel and not moving.
For a whole bunch of interesting information on MPG (much geared to OTR drivers of Semi's, but much useable for our FT's) go to this link
http://www.everytime.cummins.com/every/misc/mpg.page? (http://www.everytime.cummins.com/every/misc/mpg.page?)
Then click on the words "Check out Dr. Diesel's Secrets to Great MPG" which are in red text.
Here is the Cliff notes from the 37 pages: Enjoy -
Tim Fiedler
Rock-Solid Rules
Every 2% reduction in aerodynamic drag results in approximately 1% improvement in fuel economy.
Above 55 mph, each 1 mph increase in vehicle speed decreases fuel economy by 0.1 MPG.
Worn tires provide up to 7% better fuel economy than new tires.
Used lug drive tires can get up to 0.4 MPG better fuel economy than new lug tires.
Ribbed tires on the drive axles provide 2% better fuel economy than lugged tires.
Every 10 psi that a truck's tires are underinflated reduces fuel economy by 1%.
The break-in period for tires is between 35,000 and 50,000 miles.
Tires make biggest difference in MPG below 50 mph; aerodynamics is the most important factor over 50 mph.
The most efficient drivers get about 30% better fuel economy than the least efficient drivers.
Idle time is costly. Every hour of idle time in a long-haul operation can decrease fuel economy by 1% because you're burning fuel and not moving.
Title: Re: MPG
Post by: Dave Head on July 21, 2010, 11:21:47 pm
Post by: Dave Head on July 21, 2010, 11:21:47 pm
Sweet spot in both my C8.3 4 speed and the M11 400 6 speed are essentially the same - 62-63 mph. With the 'light' 95 model (non slide, non retarder, non Aquahot) I can squeeze 9.5 mpg on a flat road with no headwind.
There are so many variables you will only arrive at you average mpg over 'several' tankfulls.
For Silverleaf electronic coaches, maintaining forward speed with the least boost pressure and slow, consistent pedal application will always be your keys to best mileage. After that - wind, % on in town driving, tire pressure, etc etc intrude.
Oh - and now that I'm towing a Tahoe 4 down 9.5 mpg is a dream. 8.5 to 9 mpg is my new norm.
It's all right - love that Tahoe!
There are so many variables you will only arrive at you average mpg over 'several' tankfulls.
For Silverleaf electronic coaches, maintaining forward speed with the least boost pressure and slow, consistent pedal application will always be your keys to best mileage. After that - wind, % on in town driving, tire pressure, etc etc intrude.
Oh - and now that I'm towing a Tahoe 4 down 9.5 mpg is a dream. 8.5 to 9 mpg is my new norm.
It's all right - love that Tahoe!
Title: Re: MPG
Post by: Virginia on July 21, 2010, 11:31:47 pm
Post by: Virginia on July 21, 2010, 11:31:47 pm
RPM's - today towed the Matrix down to meet the Sattler's who bought her from us in Cleveland, TX a 95 mile run - I watched the RPM's at varing speed of 64 to 72 and the RPM's only wavered from 1250 to 1400 and the 1400 was when passing - Mainly was just a touch below the 1300 line - Returning and not towing the RPM's were more 1200 and was mainly rolling at 74 -
Note on a tow vehicle with distance/speed limitation - yes there are several popular ones but there are quiet a few without this huge restriction - IMHO I just can't understand why someone would buy a tow with these restriction - I've enjoyed being able to run long hauls and pass without this - Now I'm going to my truck and thou I've not looked up to see if I'm going into any restrictions, my love of my truck blinds me to this so I may be joining the club of those controlled by distance/speed limitations, until I find out tomorrow I'm ambivalently happy to know I've got my truck - Jim just shakes his head at having a crazy broad for a wife: his quote: "he is just along for the ride" :D
BTW - tomorrow we will see Camp FOT FINALLY in the rear view monitor as we head north to Athens, Tx to pick up truck then head over to central TX for DR Appts -
Please know the last 3 + weeks at camp FOT were needed to work us in for several tiny things I found and to make ready to tow truck, but they have been a struggle to as we're so past it being at a concrete lot - Results of it all though we are thinking of coming back and look for a piece of land to buy this is kinda a neat place and folks are really nice. :o ??? ::) :)
Note on a tow vehicle with distance/speed limitation - yes there are several popular ones but there are quiet a few without this huge restriction - IMHO I just can't understand why someone would buy a tow with these restriction - I've enjoyed being able to run long hauls and pass without this - Now I'm going to my truck and thou I've not looked up to see if I'm going into any restrictions, my love of my truck blinds me to this so I may be joining the club of those controlled by distance/speed limitations, until I find out tomorrow I'm ambivalently happy to know I've got my truck - Jim just shakes his head at having a crazy broad for a wife: his quote: "he is just along for the ride" :D
BTW - tomorrow we will see Camp FOT FINALLY in the rear view monitor as we head north to Athens, Tx to pick up truck then head over to central TX for DR Appts -
Please know the last 3 + weeks at camp FOT were needed to work us in for several tiny things I found and to make ready to tow truck, but they have been a struggle to as we're so past it being at a concrete lot - Results of it all though we are thinking of coming back and look for a piece of land to buy this is kinda a neat place and folks are really nice. :o ??? ::) :)
Title: Re: MPG
Post by: Tim Fiedler on July 21, 2010, 11:40:19 pm
Post by: Tim Fiedler on July 21, 2010, 11:40:19 pm
2003 Honda Element Towed generally run at 75 MPH behind the U-320. No Problems in three years and 40,000 miles towing. I pretty much figured it might be a liability disclaimer from their lawyers.
I guess I am just the guy who pushes it a bit.
Tim Fiedler 200 U-320 4010
I guess I am just the guy who pushes it a bit.
Tim Fiedler 200 U-320 4010
Title: Re: MPG
Post by: John S on July 22, 2010, 03:18:03 am
Post by: John S on July 22, 2010, 03:18:03 am
My Wrangler has been pulled behind the various coaches I have had for almost 300K miles. No issues with speed or distance, just way too many sets of tires for a vehicle with 37K miles on the clock....
Title: Re: MPG
Post by: Dave M (RIP) on July 22, 2010, 09:55:53 am
Post by: Dave M (RIP) on July 22, 2010, 09:55:53 am
We also tow the Element 04, no problem as long as you follow the directions to the T.
Been towing the Ford F150, 5 speed, Ford claims that is not possible, Remco says unlimited with the Mazda 5 speed.
So far the F150 been toad 5 K miles and still a happy shadow.
I find Remco is the source of answers that work, clearly Ford has no idea and hiding behind the legal fence.
FWIW
Dave
Been towing the Ford F150, 5 speed, Ford claims that is not possible, Remco says unlimited with the Mazda 5 speed.
So far the F150 been toad 5 K miles and still a happy shadow.
I find Remco is the source of answers that work, clearly Ford has no idea and hiding behind the legal fence.
FWIW
Dave
Title: Re: MPG
Post by: Peter & Beth on July 22, 2010, 01:25:36 pm
Post by: Peter & Beth on July 22, 2010, 01:25:36 pm
I agree that due to filling habits getting a tankfull's MPG is iffy. Here are my stats since I've owned the coach (May 2003):
Miles, 32,921
Gals, 3,974.817
Cost, $8,333.23
Hours, 204
MPG, 8.282
This is inclusive of genset usage, towing & not towing.
Miles, 32,921
Gals, 3,974.817
Cost, $8,333.23
Hours, 204
MPG, 8.282
This is inclusive of genset usage, towing & not towing.
Title: Re: MPG
Post by: Pierce & Gaylie Stewart on August 06, 2010, 11:10:04 am
Post by: Pierce & Gaylie Stewart on August 06, 2010, 11:10:04 am
We have logged just over 10,000 miles on our 93' U300/36/Detroit this last year including a trip across the U.S. and a trip to Yellowstone. We live in the California Sierra Nevada foothills with nothing but hills and curves everywhere we go so our trips are usually with minimum water, empty holding tanks and 10-15 gal. propane. The fuel mileage varies greatly with the speed, terrain and amount of city driving with 6 mpg common along the twisty California coast highways and San Francisco city driving to 12 mpg driving across the states on flat highways at 55-58 mph. Driving against the governor at 82 mph on flat road dropped the mileage down to just over 7.5 mpg. With our RAV4 behind us, the mileage is down just a little on flat road but over 1 mpg in the mountains on our trip to Yellowstone. We met a U300/40 owner in the park who in 5 years of ownership, averaged right around 8 mpg. We run 110 psi cold in the tires. This is a bit of a trade off for ride comfort with all the terrible highways here in California but the coach handles well, stops well, gets good mileage at this pressure. After all this, we look for the cheapest fuel, either on the net or going down the road, buy it and just have a good time with a great coach.
Pierce & Gaylie Stewart
93' U300/36
Pierce & Gaylie Stewart
93' U300/36
Title: Re: MPG
Post by: PatC on August 06, 2010, 12:19:28 pm
Post by: PatC on August 06, 2010, 12:19:28 pm
Don't have a computer to help me figure it out, but got 11.5 mpg when we brought the '94 U225 home. That was coming up I-75, I-77, I-71 from Knoxville, Tn. Was pulling the Focus. Tryed to stay between 60 and 65 mph. Not taking any long trips until early March, so will not have any better ideas of what is what until then.
Title: Re: MPG
Post by: Peter & Beth on August 06, 2010, 12:27:29 pm
Post by: Peter & Beth on August 06, 2010, 12:27:29 pm
Pat, does your U225 have the Cummins 5.9 engine? If it does, you should get good fuel economy.
Title: Re: MPG
Post by: wolfe10 on August 06, 2010, 05:31:48 pm
Post by: wolfe10 on August 06, 2010, 05:31:48 pm
Peter,
Yes, the U225 has the Cummins B engine (230 HP and 4 speed hydraulic Allison).
Both it and the U240 (Caterpillar 3116 (250 HP and Allison 6 speed MD3060 transmission) get 10+ MPG.
We have averaged 11.3 MPG for the 120,000 miles we have driven our coach.
Brett Wolfe
Yes, the U225 has the Cummins B engine (230 HP and 4 speed hydraulic Allison).
Both it and the U240 (Caterpillar 3116 (250 HP and Allison 6 speed MD3060 transmission) get 10+ MPG.
We have averaged 11.3 MPG for the 120,000 miles we have driven our coach.
Brett Wolfe
Title: Re: MPG
Post by: Barry Beam on August 06, 2010, 06:58:52 pm
Post by: Barry Beam on August 06, 2010, 06:58:52 pm
Quote
We have averaged 11.3 MPG for the 120,000 miles we have driven our coach.
Brett,
Suddenly I feel ill & jealous :(
Title: Re: MPG
Post by: wolfe10 on August 06, 2010, 07:08:15 pm
Post by: wolfe10 on August 06, 2010, 07:08:15 pm
QuoteWe have averaged 11.3 MPG for the 120,000 miles we have driven our coach.
Brett,
Suddenly I feel ill & jealous :(
And us "van" owners sometimes feel jealous of you big, high HP rigs.
Brett
Title: Re: MPG
Post by: PatC on August 06, 2010, 10:01:12 pm
Post by: PatC on August 06, 2010, 10:01:12 pm
Pat, does your U225 have the Cummins 5.9 engine? If it does, you should get good fuel economy.
Title: Re: MPG
Post by: Peter & Beth on August 06, 2010, 10:22:36 pm
Post by: Peter & Beth on August 06, 2010, 10:22:36 pm
Hey Pat...bottom line...you can get from point A to point B a lot cheaper than most of us... :))
Title: Re: MPG
Post by: Jerry Whiteaker on August 07, 2010, 11:01:03 am
Post by: Jerry Whiteaker on August 07, 2010, 11:01:03 am
I added up all the diesel I have purchased; deducted .4 gal for each hour of generator run time, and came up with 8.5 mpg. This is what a previous owner said he averaged. Prior to my last trip, I had not been paying much attention about using the econ mode (mode on) with the transmission. For that trip of 3005 miles, I was in econ mode almost all the time. It was also a lot of up and down, secondary roads, over Monarch pass at 11,000 ft, and average mpg was 8.46. I will definitely be using the econ mode from now on. Cummins 8.3 mechanical engine with 3060R transmisision and towing a 3000 lb Subaru Forester from day one.
Jerry Whiteaker
96 U270 36'
Jerry Whiteaker
96 U270 36'
Title: Re: MPG
Post by: Larry Bradley on August 07, 2010, 12:37:08 pm
Post by: Larry Bradley on August 07, 2010, 12:37:08 pm
I guess I need to learn to drive different.
Just done a 2000 mile trip to Colorado from Texas.
Average 7.1 Generator running when traveling, average speed 65 to 68 Mph on interstate.
1900 RPM.
Larry Bradley
98 u270
Jeep Toad
Just done a 2000 mile trip to Colorado from Texas.
Average 7.1 Generator running when traveling, average speed 65 to 68 Mph on interstate.
1900 RPM.
Larry Bradley
98 u270
Jeep Toad
Title: Re: MPG
Post by: wolfe10 on August 07, 2010, 02:08:34 pm
Post by: wolfe10 on August 07, 2010, 02:08:34 pm
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 (https://ohe.cat.com/cda/files/287140/7/LEGT5364.pdf)
Brett Wolfe
Brett Wolfe
Title: Re: MPG
Post by: Dwayne on August 07, 2010, 02:25:20 pm
Post by: Dwayne on August 07, 2010, 02:25:20 pm
On my recent cross country trip I only checked it for a few tank fulls. When driving 70 mph I am getting around 9.5 but if I keep it down to around 60ish I get about 10.5. I don't think I'd get to 11.5 unless I was driving a very religious 55 or under. But let me say that running the LP generator all the time offsets any fuel savings. I was buying about a half to three quarters of a tank of propane every other day when staying at the Flying J or Crackle Barrel overnight.
Title: Re: MPG
Post by: J. D. Stevens on August 07, 2010, 02:50:07 pm
Post by: J. D. Stevens on August 07, 2010, 02:50:07 pm
We have put about 5,000 miles on our 1997 U295 36'. Mileage was about 61,000 when we bought the coach in April. We have run the generator a large part of the time while driving. We have pretty consistently shown 7 mpg based on odometer differential/gallons to the tank. I don't adjust for the generator. We drive 60-65 mph, and tow a Grand Cherokee. Gross weight of the combination was measured at 32,280#. The engine is C8.3 325 (mechanical) with a Banks stinger (I think). The exhaust blows a puff of smoke on initial acceleration, but is otherwise clear. The boost and pyrometer show "normal" readings for conditions. All gauges values show nominal values.
I was expecting about 8-8.5 mpg, and surprised that we only measure 7 mpg. Our previous coach was 21,000# with a C5.9. We got 9-10 mpg with that coach.
I was expecting about 8-8.5 mpg, and surprised that we only measure 7 mpg. Our previous coach was 21,000# with a C5.9. We got 9-10 mpg with that coach.
Title: Re: MPG
Post by: John Cooper on August 08, 2010, 10:47:09 pm
Post by: John Cooper on August 08, 2010, 10:47:09 pm
Larry,
1. You were going uphill (most of Colorado is higher than most of Texas).
2. Slowing down 5 mph would help.
John Cooper
'91 GV 36'
---
1. You were going uphill (most of Colorado is higher than most of Texas).
2. Slowing down 5 mph would help.
John Cooper
'91 GV 36'
---
Quote
On Sat, 8/7/10, Larry Bradley Wrote:
I guess I need to learn to drive different.
Just done a 2000 mile trip to Colorado from Texas.
Average 7.1 Generator running when traveling, average speed 65 to 68 Mph on interstate.
1900 RPM.
Larry Bradley 98 u270
Jeep Toad
Title: Re: MPG
Post by: Dick Kinsler on November 28, 2010, 06:15:02 pm
Post by: Dick Kinsler on November 28, 2010, 06:15:02 pm
Just to put my oar in the water, my coach (a '98 40 ft, U320) came with a fuel consumption chart (bsfc chart) for the M11 engine. It showed minimum fuel consumption between 1300 and 1400 RPM. This translates to about 62 or 63 mph in 6th gear. This is just above the shift point of the transmission. Generally, I seem to run about 8 mpg at that speed. I would be surprised to get better mileage at 70mph. I don't think the aerodynamics of the coach would allow it, unless you are running down a very long hill or have a very good tailwind.
Title: Re: MPG
Post by: nitehawk on November 28, 2010, 07:13:45 pm
Post by: nitehawk on November 28, 2010, 07:13:45 pm
When we first took our '89 GV on a trip we were so enamored with the fact that at 55MPH it felt like we were sitting still! We seemed to have time to almost "stop and smell the roses" so we have continued the 55MPH with occasional deviations. These deviations occured when I didn't pay attention to the speedometer.
Because our fuel gage didn't work accurately I monitored the consumption rate and did a comparison to our gas 31' class C with both rigs towing our toad. We went from 4.5MPG to 8.87MPG. I dumped a gallon of Lucas Injector cleaner in the fuel tank and power went up significantly, so much so that I had to watch my speed closer. We also increased MPG by .5MPG.
Still, the only reasons we watch the MPG is because we do not trust the fuel gage, changes in MPG may be indicative of problems, and we don't want to run out!!
Because our fuel gage didn't work accurately I monitored the consumption rate and did a comparison to our gas 31' class C with both rigs towing our toad. We went from 4.5MPG to 8.87MPG. I dumped a gallon of Lucas Injector cleaner in the fuel tank and power went up significantly, so much so that I had to watch my speed closer. We also increased MPG by .5MPG.
Still, the only reasons we watch the MPG is because we do not trust the fuel gage, changes in MPG may be indicative of problems, and we don't want to run out!!
Title: Re: MPG
Post by: George Stoltz on November 28, 2010, 08:48:51 pm
Post by: George Stoltz on November 28, 2010, 08:48:51 pm
On Sun, Nov 28, 2010 at 5:15 PM, Dick Kinsler
Quote
Just to put my oar in the water, my coach (a '98 40 ft, U320) came with a fuel consumption chart (bsfc chart) for the M11 engine. It showed minimum fuel consumption between 1300 and 1400 RPM. This translates to about 62 or 63 mph in 6th gear. This is just above the shift point of the transmission. Generally, I seem to run about 8 mpg at that speed. I would be surprised to get better mileage at 70mph. I don't think the aerodynamics of the coach would allow it, unless you are running down a very long hill or have a very good tailwind.
Title: Re: MPG
Post by: Dave M (RIP) on November 29, 2010, 01:30:57 am
Post by: Dave M (RIP) on November 29, 2010, 01:30:57 am
Another oar in the water, Since the coach is in the Xtreme shop this past month, I have been driving my toad/frog, Nac to Va 1210 miles each way. Now returning, currently in a Motel 6 Chattanooga, Tn.
I find it interesting, driving the F150 Ford instead of towing it, how maneuvering it so simply on the highway after the coach. Find traveling at 75-80 mph seems to be the norm these days. What is truly interesting every time I refuel it, I laugh, I fill it all I can get in the tank every time, right to the over fill level. Fuel mileage has been steady at 22.5 to 23.59 mpg. I say WOW :))
Admit it is a light duty pickup, 4.2 V-6 with the 5 speed Mazda gear box and empty.
Have been totally amazed because I expected to blow it up running like that, the only thing that happened, it now runs so much better, even perfect, smoother, burns zero oil, perfect frog. Reminds me of a Chevy 283 power wise, very spunky :)
I find it interesting, driving the F150 Ford instead of towing it, how maneuvering it so simply on the highway after the coach. Find traveling at 75-80 mph seems to be the norm these days. What is truly interesting every time I refuel it, I laugh, I fill it all I can get in the tank every time, right to the over fill level. Fuel mileage has been steady at 22.5 to 23.59 mpg. I say WOW :))
Admit it is a light duty pickup, 4.2 V-6 with the 5 speed Mazda gear box and empty.
Have been totally amazed because I expected to blow it up running like that, the only thing that happened, it now runs so much better, even perfect, smoother, burns zero oil, perfect frog. Reminds me of a Chevy 283 power wise, very spunky :)
Title: Re: MPG
Post by: ncaabbfan on November 29, 2010, 11:42:16 am
Post by: ncaabbfan on November 29, 2010, 11:42:16 am
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 (https://ohe.cat.com/cda/files/287140/7/LEGT5364.pdf)
Brett Wolfe
I am not able to access the referenced article. Can others access it?
Thank you.
Title: Re: MPG
Post by: wolfe10 on November 29, 2010, 12:39:22 pm
Post by: wolfe10 on November 29, 2010, 12:39:22 pm
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 (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 (http://f1.grp.yahoofs.com/v1/ENzzTKLhVJ6YlEHx00b2bR6_cukrzTdNpjjvwR0Iihg2BwJdroJYywJCOsZk_al8crafzrXO1MyTrCIYFMT7gw/Understanding_Coach_RV_Performance.pdf)
Brett Wolfe
Title: Re: MPG
Post by: ncaabbfan on November 29, 2010, 01:57:58 pm
Post by: ncaabbfan on November 29, 2010, 01:57:58 pm
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 (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 (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.
Title: Re: MPG
Post by: Dave M (RIP) on November 29, 2010, 03:29:34 pm
Post by: Dave M (RIP) on November 29, 2010, 03:29:34 pm
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.
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.
Title: Re: MPG
Post by: ncaabbfan on November 29, 2010, 03:34:19 pm
Post by: ncaabbfan on November 29, 2010, 03:34:19 pm
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.
Title: Re: MPG
Post by: Barry Beam on November 29, 2010, 03:54:46 pm
Post by: Barry Beam on November 29, 2010, 03:54:46 pm
Unfortunately, I still cannot see it....get the 404 error code, page not available. Thank you very much for your effort.
Title: Re: MPG
Post by: Dave M (RIP) on November 29, 2010, 03:58:37 pm
Post by: Dave M (RIP) on November 29, 2010, 03:58:37 pm
:) 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
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
Title: Re: MPG
Post by: Chad and Judy on November 29, 2010, 04:13:37 pm
Post by: Chad and Judy on November 29, 2010, 04:13:37 pm
I've owned several fairly late-model F-150's and guessed your tongue was firmly in your cheek on the mileage claim.
Title: Re: MPG
Post by: ncaabbfan on November 29, 2010, 04:16:33 pm
Post by: ncaabbfan on November 29, 2010, 04:16:33 pm
Unfortunately, I still cannot see it....get the 404 error code, page not available. Thank you very much for your effort.Try this.
Got it!!! Thank you very much.
Title: Re: MPG
Post by: Tom Lang on November 29, 2010, 06:46:57 pm
Post by: Tom Lang on November 29, 2010, 06:46:57 pm
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).
Title: Re: MPG
Post by: Bob Raab on January 08, 2011, 01:17:15 am
Post by: Bob Raab on January 08, 2011, 01:17:15 am
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.
Title: Re: MPG
Post by: Lewis Anderson on January 08, 2011, 07:59:01 am
Post by: Lewis Anderson on January 08, 2011, 07:59:01 am
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
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
Title: Re: MPG
Post by: Dave Head on January 08, 2011, 08:52:01 am
Post by: Dave Head on January 08, 2011, 08:52:01 am
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.
Title: Re: MPG
Post by: George Stoltz on January 08, 2011, 09:44:28 am
Post by: George Stoltz on January 08, 2011, 09:44:28 am
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.
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.