MPG

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MPG

October 07, 2018, 12:32:49 am

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.

Re: MPG

Reply #1 – October 07, 2018, 07:06:24 am

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

Re: MPG

Reply #2 – October 07, 2018, 07:10:18 am

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

Re: MPG

Reply #3 – October 07, 2018, 09:31:51 am

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.

Re: MPG

Reply #4 – October 07, 2018, 09:34:17 am

Quote from: bigdog – October 07, 2018, 12:32:49 am

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.

What speed were you driving?

Re: MPG

Reply #5 – October 07, 2018, 09:43:24 am

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.

Re: MPG

Reply #6 – October 07, 2018, 09:50:11 am

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.

Re: MPG

Reply #7 – October 07, 2018, 09:52:47 am

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.

Re: MPG

Reply #8 – October 07, 2018, 09:56:53 am

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.

Re: MPG

Reply #9 – October 07, 2018, 10:22:18 am

***Understanding Coach /RV Performance***

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"

Re: MPG

Reply #10 – October 07, 2018, 11:03:12 am

Quote from: MT Ted – October 07, 2018, 09:56:53 am

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.

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

Re: MPG

Reply #11 – October 07, 2018, 11:09:40 am

Quote from: bigdog – October 07, 2018, 12:32:49 am

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.

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

Re: MPG

Reply #12 – October 07, 2018, 11:34:03 am

Quote from: wolfe10 – October 07, 2018, 10:22:18 am

***Understanding Coach /RV Performance***
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"

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

Re: MPG

Reply #13 – October 07, 2018, 11:47:58 am

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.

Re: MPG

Reply #14 – October 07, 2018, 11:53:30 am

Quote from: bigdog – October 07, 2018, 11:47:58 am

65 max Brett. Most of the time I set it at 62 where the torque converter locks up.

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

Re: MPG

Reply #15 – October 07, 2018, 12:30:47 pm

Quote from: bigdog – October 07, 2018, 11:47:58 am

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.

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

Re: MPG

Reply #16 – October 07, 2018, 12:31:07 pm

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.

Re: MPG

Reply #17 – October 07, 2018, 12:32:10 pm

Correct.

The torque converter is locked in "high 2nd" and all higher gears.

True one all Allison 3000 and 4000 series.

Re: MPG

Reply #18 – October 07, 2018, 12:45:17 pm

Quote from: wolfe10 – October 07, 2018, 12:32:10 pm

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.

Re: MPG

Reply #19 – October 07, 2018, 01:41:14 pm

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.

Re: MPG

Reply #20 – October 07, 2018, 03:34:35 pm

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.

Re: MPG

Reply #21 – October 07, 2018, 04:36:23 pm

Here's a link to fuel mileage on our 36' U320. I need to update the last couple of years.
ISM450 Fuel Mileage

Re: MPG

Reply #22 – October 07, 2018, 04:46:01 pm

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

Larry

Re: MPG

Reply #23 – October 07, 2018, 05:27:19 pm

Quote from: ohsonew – October 07, 2018, 04:46:01 pm

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

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.

Re: MPG

Reply #24 – October 07, 2018, 05:40:17 pm

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.

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