Just arrived back home from our central Washington coast trip. For the first time in my ownership. I decided to calculate my MPG. Mind you, I pull a twin axle car trailer with a 4,200lb car that has a Tandem Sea kayak and two Day6 bicycles stuck on it as well. Total trailer weight is right at 6K. I generally keep the speed at 63-65. I got 6.5 MPG. It's about what I thought I would get with that trailer. I recon that sans the trailer I should get 7-7.5.
If no wind to overcome , flat 6.5 . My average is less . I pull a three quarter ton , 4 by 4 , diesel truck hauling my 1580 pound toy and all the stuff I just got to have along with it comes up to 10, 400 pounds . So , no complaint on this issue , it is what it is . I worry about several other things like tires and the PTO on the radiator fan drive thing . And here lately the gen set ordeal . ??? ??? ??? Brad Metzger
On my way to Branson last week, I filled the tank. I had only driven 341 miles of mostly flat open highways in Eastern Kansas. The gauge showed that I was down to 5/8 of a tank. It took 37.768 gallons was all that I could squeeze in. An amazing 9.02 mpg!!!!!! I learned 2 things. (1) My fuel gauge isn't very accurate, (2) I'm certain that once I got down into the Ozark mountains that my mileage will drop. I guess we take the great with the bad. Haven't filled up since, but I hope that I can average 7-7.5 like you expect. At this point, I am not towing, so I am certain that when I start that, it should affect my totals.
Larry
When going to Glacier National Park with my F350 dually with a Lance camper in her bed; fighting the wind 4.5mpg. 38 gallon fuel tank would not get me 200 miles. I am anxious to see what my FT will do next year when I make a return trip.
What speed were you driving?
Good AM Brett
I was driving 75mph with a 10 cylinder Ford gas engine. The winds were probably over 30mph. Usually on flat land driving 70mph it would get 7.4mpg. I have never figured out what my FT with C8.3 Cummins mpg. But it does not seem like it is bad for motorhome.
Closing in on a 5,000 mile, 9 Western State trip running solo @ 27k lbs. with a 8.3 @ 300hp traveling between 62 and 72 miles per hour depending on terrain and wind conditions averaged 8.5 MPG. I find that towing doesn't affect mileage much. Possibly breaks the wind drag and I may drive a bit more conservatively.
Our 2001 U320 with an ISM11 Cummins has averaged 7.9 mpg from the day it left Foretravel. Speed, wind, weight and driving habits all affect your mpg. It will take about 20% more fuel to overcome aerodynamic resistance at 70 mph then it does to drive 64 mph. Aerodynamics takes about 50% of the total energy to move your coach. Low tiire pressure (relative to your actual weight) makes rolling resistance go way up.
When we bought our coach in CA and drove it home to MN, more than 2500 miles, the coach was essentially empty, no toad, as light as it has ever been and we got 9.6 mpg for that trip.
I get asked often, "How much fuel does your coach use?". All that I put in, I say.
Ive had my coach just over a year. I think its fun to check the mileage every fill up. Ive put over 7k miles on, she gets 7-7.1 mpg. Ive checked it towing a 28' trailer and empty it gets the same. I set the cruise at 1700 rpm and let her eat. I try and use cenex roadmaster diesel every fill up.
***Understanding Coach /RV Performance*** (http://forum.dieselrvclub.org/index.php/topic,6594.msg15141.html#msg15141)
A very good read for anyone driving a heavy vehicle. Download it from the link at the bottom of the page. Page 4 gives the FACTS on effect of speed on MPG. Page 7 gives the FACTS on effect of grade on MPG.
A Caterpillar engineer and I worked on this document for several weeks. He did the physics, I did the "how do we relate this to motorhomes-- some with vastly different weights/drivetrains.
If that link/post does not come up (I am moderator of the Diesel RV Club website as well, so my access may be different), just do a search for "Understanding Coach/RV Performance"
We have the same engine but at 36 feet, it's shorter so lighter. Since the coach was new, it has averaged exactly 8.0 mpg as the DDEC ECU reads in over 100K miles. We cruise at 1600 RPM so a little slower, keep 110 PSI on all 6 and have the toad on probably three quarters of the time. On a recent trip w/o toad, we averaged 9.95 mpg after fueling a little above sea level, driving up to Mr. Shasta and refueling at the same Casino on the way home. Another trip up to high altitude in the Sierras averaged about 8.7 w/o toad.
Check your air cleaner as you should be doing a little better than 7 mpg. You can plug in a reader and see what the computer says. A couple other Detroit owners have said that they have used the Pro-Link to read theirs and they were at 8.5 mpg over the coach's life but one was at 7.6 mpg. We live in the mountains so mileage suffers a bit so keep the water tank low until arriving at our destination and also keep grey/black tanks empty.
Even with a 3K lb. toad behind, I can easily feel the difference on grades and mpg suffers.
Pierce
Big Dog,
As you were going west I was going east, from the Tacoma area to Jackson then Yellowstone via southern Idaho, got 8.3 mpg on the first fill up and 7.7 mpg on the second. I'm usually all over the board on speed, we take a lot of twisty back roads but on the freeways its 65 to 70 mph. That's with the Cummins M11 towing a 2,000 lb sammie.
PS. fuel was 3.25 to 3.74 a gallon
Brett,
Good and informative articles especially the gain from synthetic oil in the engine as well as the transmission. Used vs. new tires is significant.
What I have not seen is any chart showing the difference between driving on the flat and lower elevations and flat terrain at higher elevations. How about flatland driving against mountain driving with western states as an example. Leaving our house and driving up over Donner Summit and down to a campground on the Truckee River drops our mileage to just over 4 mpg. We make up part of it on the way home with more downgrades than upgrades but it still suffers in the mountains.
Also wonder about a chart showing MPG differences when you have a toad behind perhaps showing differences in 1000 lb. increments. I didn't notice ours much until we hit the mountains.
Pierce
65 max Brett. Most of the time I set it at 62 where the torque converter locks up.
When i'm In this region. I fill on I-84 at pilot. They sell B-20 fuel which has a lower BTU per volume. So that can be detrimental to mpg. I would prefer full Dino diesel. But that is getting more difficult to find.
That's not your convertor locking up it is going into 6th gear. If you had the VMSpc it would show it. That is one of my issues in Cal. trying to stay with the 55 mph speed limit while towing.
t
USLD (Ultra Low Sulfur) has a BTU content of 138.490 BTUs/Gal while B-100 (100% Biodiesel) has a BTU content of 127,960 so B-20 has about 99% of the energy content of petro diesel. On top of that, the cetane rating is higher for biodiesel which means easier starting. Wintererized petro diesel is a blend of number 1 and 2 diesel so has a lower energy content but is less viscous so more efficient at lower temperatures.
At 99 percent of the energy, I think it's very hard to detect any mpg difference with B-20 plus the biodiesel produces less particulate emissions and may allow faster and easier starting in cold temperatures. We fuel with either B-5 or B-20 where we live and don't see any mileage difference.
https://www.afdc.energy.gov/fuels/fuel_comparison_chart.pdf
Pierce
Our 97 u320 shifts into 6th at 55 normally.
Last 12k miles since the resonator and fan drive mod the VPMS shows 8.1 mpg. Towing 4K. full of everything. 70 mph towing. Tried 60 and 65 mph and could get over 9 mpg easily but too much time lost on a 500 mile day for me.
We have to climb grades to leave LA. Plus crowded freeways.
Correct.
The torque converter is locked in "high 2nd" and all higher gears.
True one all Allison 3000 and 4000 series.
I didn't realize that was the case. learn something new all the time.
Jerry, with your transmission in normal mode (mine anyway) 62 mph is just at the point it shifts from 5 to 6. At 63 or 64 you are more likely to stay in 6th. 1380 rpms is about the sweet spot for the M11. If you switch the transmission mode to econ then the up shift points drop a bit and the down shift point a bit more. So with not much trottle load you will upshift closer to 60 and downshift as low as 57 or 58 depending on load. Econ mode is best used is fairly flat terrain.
I can always see a performance difference when not towing. Not towing rarely happens.
MPG is a long term thing. Months or years. Tank to tank or even a few days is within normal variations. We got 11.5 mpg over two days from Denver to HWH, 700 miles. Nice tailwind. We have hit 6.5 over a couple days too with big headwinds in OK. If you are watching for a change because of a mechanical issue or something other than normal driving conditions it needs to be over a couple months or several thousand miles.
To be honest Roger. I haven't even been keen to check my MPG. As it will be a narrow range of Terrible to slightly less terrible. But in reality. It wasn't as bad as it could have been.
When I went to Seattle to pick up my Caterham Super 7 at the port. I borrowed a friends truck (chevy 8500 dually) which had a 502 big block four barrel carb. Towing an empty car trailer 7MPG, towing a car trailer with a car on it 7MPG. Driving without a car trailer 7.5 MPG. That thing really liked gas no matter what it was doing. So 6.5 in a coach hauling a lot of weight actually is not as inefficient as it sounds. My class 8 truck hauling two trailers running a Cat C15 (550HP 2000 Ft Lbs) got 5MPG.
Here's a link to fuel mileage on our 36' U320. I need to update the last couple of years.
ISM450 Fuel Mileage (http://www.foreforums.com/index.php?topic=29320.msg248112#msg248112)
Bigdog, I know the feeling. I had an 89 3/4 ton Suburban. 8 MPG empty or towing my 25' boat, didn't matter. I sold it when the price of gas hit the unbelievable price of $1.25/gallon. Don't we wish we could go back :D
Larry
I'd like to go back and undo some of the crap I shouldn't have done. But then again, Those are some of the things where one learns the biggest and longest lasting lessons.
Yet I'd love to go back to 1980 and stop myself from selling my 1969 Corvette convertible.
When I first used my '78 Vogue it got 4 1/2 mpg. I changed the cam, intake added Doug Thorley headers, MSD ignition and adjustable timing. Got it up to 7+ mpg. I believe it was about a 23,000 GVW. now with the 34,880 GVW. Foretravel, get around 8 mpg. Sometimes things get better.
Jerry, I worried about MPG for a while after we got our coach, but it is whatever it is going to be. I try to drive carefully but I can't so anything about wind and other factors. I am still averaging just under 8 and am pretty happy about it. We are staying longer where we get to so our miles per day is getting less as is fuel $ per day. Of course if you never went anywhere it would go to zero but that is no fun.
Our 40 ft 1995 U320 with 400 Hp Cummins M11 and Aqua-Hot gets between 7 and 8 MPG overall while towing our Chevy Equinox an traveling at about 70 MPH over a wide variety of terrain and weather conditions.
I've never concerned myself with MPG's, but rather with the range with the diesel left in the tank. I like to know how far and when I need to get fuel.
Now on my cars & trucks I track MPG's in order to see if there is a problem creeping up.
Same here. I don't worry about it to much. however, Just like Han Solo, I try to "fly casual" and that is usually a good way to be economical with out whipping out a calculator.
I still need to get a vms from you.
Kansas appears flat, but going eastbound the elevation drops about 10 ft every mile. So your running slightly downhill. Just the erosion deposits from the Rocky mountains.
Looked up Texas on a globe, and figured we would get better mileage going down than coming back. And I was right!!
Downhill one way and uphill coming back.
31480 lbs+ 4700 towed, gets 8MPG@ 65 mph. Don't worry much about it though just put them dinosaurs in the tank and light em up. 👍😎🌵
My old coach because it's 6" narrower and at least a foot shorter heightwise And a sloped nose will run 10-11mpg at 65 all day long.
Roger, "but it is whatever it is going to be." is so true. My 92 Signature had fuel tracked since new, previous owner always got 10 mpg. After purchasing it, I always got 8 mpg and I'm an easy driver. I do tow a 5500 to 6000 lb dingy, I used the generator often to charge the batteries, and often ran the A/C while dry camping with the generator running. My FT when I checked it on last years 2500 mile trip I got approx 8 mpg, and yes, ran the a/c allot with the generator running instead of being plugged in.
Jack,
More likely the P.O. "claimed" he got 10 mpg. 8 mpg for a 40 foot 102 inch coach w/toad is nothing to sneeze at a 60-65 mph cruising speed.. The lower, 96 inch coaches push less air and are lighter so 10-11 mpg is probably pretty normal. Side radiator coaches use somewhere around 35 hp to run the fans at 65 mph and up to 60 hp on grades. That's a lot of fuel wasted.
MPG off the ECU is almost always less than operator claimed.
Pierce
When I bought the coach ten years ago, the ecu reported 8.5mpg overall. Now it reports 7.5
The first owner probably drove like an older lady, and for good reason. I like to hot rod a bit.
Lately I've slowed down. Driving my age? vmsPC is frequenty reporting averages around 9.
Tom,
Was the P.O. also on the west coast? With all the mountains and rugged terrain here, mileage will be less. I'm at full throttle quite a bit of the time from stop signs, grades, but find that about 60-65 on the freeway and less on 395 allows me to spend more time looking around rather than having to focus so much. Speeds like the blowout RV was traveling at are not what retirement is for.
Our air cleaner restriction gauge was at the end and after changing the element, we got both more power and better mileage.
Pierce
When I drove the coach empty from Nac. to Chicago I got a little under 10 mpg. Similar to Rodger but without the mountains. I was not going slow either. Driving style has a lot of influence on MPG. The harder you mash the pedal the more fuel you will use. Loaded towing the CRV at 65 mph I get about the same on flat terrain. In town it's abysmal.
Keith
I started keeping mileage records a couple of years ago. We're at 6.7 overall at this time, with about half of that on the old engine and half on the rebuilt one. The generator is usually running on travel days, and I don't make any allowance for that. I figure that I still have to put that diesel in the tank, so that is part of operating the coach.
Roger is sending the VMSpc stuff, so by the time we leave at the end of the month I'll have that all hooked up and running. Then maybe I'll have a different number to report. In the meantime I'm happy with what we get.
Ol' Moby did 11 on our big 2500 mile Yellowstone trip. I haven't really kept track of mpg since then.
Left NAC with a "ton" of "coach bucks " left behind . Sort of expected a big improvement in this MPG thing . Hmm----no change , same five and a half to six . ::) ::) ::) Brad Metzgert
If you have a big wide and long coach with slide and a flat nose, you can't expect much better than that and can't compare it to GVs with the low and narrow body. The CATs and 5.9 Cummins are going to almost double your mileage even without tranny lockup. Plus, you have a trailer on behind as I remember. Will drop more in the Rockies.
PIerce
No surprise here , no change either . This coach has the aerodynamics of a shoe box . The only way it could get better would be down hill every where you went . So , am very aware of this aspect , I buy fuel , moan and keep on doing what I intended to do in the first place . My goal from day one is to ware this thing out . Looks like it will outlast me with no problem . Every issue with this coach has been resolved . The day will come when someone will get a coach that has been looked after . Brad Metzger
Like Brad said, don't have to like the price of fuel, but it's the cost of doing business.
It's the dishwasher Brad. Way too heavy
Yet at the same time. There's no reason a person shouldn't try differing driving techniques to maximize their MPG. Tossing a rock on the go pedal and calling it good is of course one way to drive. But YMMV. One way to look at it is that going from 6.5 to 7.5 mpg is a 15% reduction in fuel costs. That equals NOT having to buy 29 Gallons to refill my 197 Gallon tank. That adds up.
I do the MPG game in my Mercedes SUV. I can drive it like I rented it and get 37 mpg. But by being just a bit careful. I've seen 47 mpg in a 4,200Lb full time awd suv. And routinely get 41-42mpg.
True. .5 MPG makes a few dollars in the pocket.
If we moved the horns back to a low pressure area, added a better slope to the front AC unit and maybe added a front air dam... I could see anouther .5 or better. IMHO.
One of the reasons I max the tire pressures and make sure the front end has just a little toe in. Having a lower RPM cruise in not in the cards for our four speed Allison but the lockup helps.
Tire air pressure just to taxi an aircraft makes a big difference. With low pressure, lots of throttle is needed just to get it rolling and it takes a couple seconds longer to get off the ground. With the tires pumped up, you have to be careful when taxiing downwind as a following wind will push you along.
The hydraulic fans are the big thieves here. Anywhere from 35 hp at cruise to 65 hp on grades at high RPM drops the mpg way down. A 65 mph cruise probably takes (just guessing) about 150 hp on flat ground for a 102 inch coach so 35 hp is a big deal. With a GV, twin front radiators with electric fans when the ram air is not effective like around town would save not only fuel but thousands of coach bucks when a failure occurs. A hydraulic failure can also be associated with engine overheating and damage too.
Pierce
Are our fans always on? or are they on a demand basis?
Should be LOW-HIGH, not ON-OFF.
Even if coolant temperature is not high, you still need air flow through the CAC.
Always on, speed varies based on demand
Early coaches had an low or high fan speed control. Later coaches have a variable speed piloted wax capsule fan control. Mechanical. No electricity
Update.
Trip to Leavenworth Washington today. Fresh Cat 3126 engine......I saw a lot of this. Flat road, no tow vehicle, full of fuel and water. NO tail wind, NO head wind. 62 MPH. 1700 or so RPM's is the sweet spot
Up from 6 to 6.5 with sick engine.
Chris
Just did a trip from Loveland CO to White Pigeon MI and back, a little over 2,220 miles total. Was not towing anything, mostly on I-80 East and West...
To White Pigeon I averaged 9.5 miles per gallon @ 65/67mph
Back to Loveland I averaged 8.0 miles per gallon @ 62/65mph
Configuration:
empty Black/Gray/Fresh Water tanks
very little accessories since I've not had the time to outfit my RV
v/r Bob
Mechanical cummins (like my 8.3) have the wax capsule control deal. The newer electronic (99or 2000 on) 8.3s have a solenoid valve for high/low...as do the m11. Ironically, a guy on the internet makes a kit to convert the electronic engines to the wax capsule control LOL. My fans barely spin when the engine is cool.
The issue with the electronic high low is when it fails it goes to high speed. I would convert mine to the wax capsule if it did not already have it.
I compliment Gracerace for the 63 mph. I tow at 70 and hit the hills floored. Average for the last 12k Miles is 8.1 mpg
What does the "wax capsule" on your coach look like? I'd really like to see a photo of it.
AFAICT, our '93 does not have
any kind of 2-speed device. I have looked closely at each of the hydraulic hoses between the hydraulic pump and the fan motors. I can't see anything that looks like a speed controller. I
think on our coach, the fan speed is controlled by the hydraulic pump speed, which is determined by the engine speed. Higher engine RPM = higher fan speed.
You should be getting better milage than that. Do you have the roof storage pod? Any black smoke? Engine temps low? My cat runs 10.8 to 11.1 at 65 to 68.
The difference between the 250 hp and 300 hp makes the 250 work harder. I had the same issue on one of my cranes 53,000 lbs. 350 hp 7mpg, my last one 31,000 lbs 210 hp 5.2 mpg.
Could be headwinds, tire pressure, alignment, air cleaner or a combination of these. With a narrow body and light load, it should be at least one mpg better. Sometimes headwinds seem to follow you around. They make a huge difference.
Pierce
Or the rings are not seated totally. My m11 was mentioned on the trucker pages to not seal up until 150k miles.
The lower back pressure resonator I think added some final ring break in. No way to verify other than seat of the pants dyno.
Drive it like you stole it. Maybe a chassis dyno run?
Fuel system might need attention. Translation: turn it up.
How's your fuel lines? Cracked lost power and mpg