MPG

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

MPG

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.

Re: Re: MPG

Reply #1 – 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.

Re: Re: MPG

Reply #2 – 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

Thru software maybe on the electronic engine?

Re: Re: MPG

Reply #3 – 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

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

Re: Re: MPG

Reply #4 – 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

Re: Re: MPG

Reply #5 – July 20, 2010, 07:27:05 pm

Quote from: Paul Smith – 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

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.

Re: Re: MPG

Reply #6 – 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.

Re: Re: MPG

Reply #7 – 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.

Re: Re: MPG

Reply #8 – 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.

Re: Re: MPG

Reply #9 – 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

Re: Re: MPG

Reply #10 – July 20, 2010, 09:13:12 pm

Just for giggles

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

Re: Re: MPG

Reply #11 – July 20, 2010, 10:02:16 pm

Dave,

Amen

Re: Re: MPG

Reply #12 – 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.

Re: MPG

Reply #13 – 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)

Re: MPG

Reply #14 – 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.

Re: MPG

Reply #15 – 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).

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)

Re: Re: MPG

Reply #16 – 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?

Re: MPG

Reply #17 – 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.

Re: MPG

Reply #18 – 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

Re: MPG

Reply #19 – 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.

Re: MPG

Reply #20 – 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

Re: MPG

Reply #21 – 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

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.

Re: MPG

Reply #22 – 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

Re: MPG

Reply #23 – 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?

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.

Re: MPG

Reply #24 – 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!

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