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JohnJill

Fuel Mileage

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Here I am again, looking for advise from my seniors. We have a 2007 40ft Meridian 400hp cat. Looking for any trick to improve my miles per gallon. Right now I'm about 6.9 empty 6.6 towing. Coach has been services oil, fuel filter, tire pressure. Either mileage is at speeds of 62 and even bumped it up to 70 still 6.9mph. Any tricks of the trade.

Thanks Again

John

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John,

How many miles on the coach?

Air filter minder reading?

What is coach weight? Toad weight?

Do you drive in "economy mode"?

At what speed do you go into 6th gear? what RPM?

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If your mileage is the same at 70 as it is at 62, you may be experiencing one of the following conditions. Your mileage is probably:

1. Understated at 62

2. Overstated at 70

My guess is you weren't experiencing the same conditions of headwinds, tailwinds, terrain, etc. On my coach and most I have heard of, there would be a major difference in mileage at the speeds you are quoting. But hey, I guess anything is possible. I've had motorhomes for 35 years and 70 mph isn't in my comfort zone. 62 is what I usually run..... But I can notice a decrease in mileage at 65.

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There is 31,000 miles on it all of the fluids and filters have been change less than 500miles ago. There is not a economy mode on this 6th gear I'm turning about 1500. And it could be my computer reading I have not checked it the non technology way, but will

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John,

All Allison 3000 and 4000 transmissions have an economy mode option (button on shift pad labeled "MODE").

Please DO check mileage the "old fashion way" (miles divided by gallons less fuel used by generator). The computer can be well off.

You are approaching the first scheduled valve adjustment for your engine. If the valves are out of adjustment, that can cause lowered MPG and HP.

Air filter minder reading?

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I do have a Allison transmission not sure what series. Never seen a mode button on the electric shift plate

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I do find a good bit of difference between computer mileage and actual "old fashioned way" of figuring it. On one trip as much as 1 MPG difference with computer showing the lesser of the two. That said, i see bigger difference in speed variations than whether or not I am towing. At 62 to 65 MPH i seem to get in the 7.5 MPG range on average but at higher speeds like 70, i was closer to 6.8 when traveling relatively flat terrain. only .3 MPG or so difference when towing. I have gotten as high as 8.1 on trip from WV to Indy traveling light and 7.8 with toad at the lower speed and no AC. As stated by Planocat, my comfort zone has dropped to the 62 to 65 range and my pocket book seems to agree.

I am running a 400HP Cummins w/ Allison tranny in a 40ft Holiday pulling a Jeep Liberty.

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John, watch Planocat, he just got his drivers license.

Some times I think Brett has his sail up when he has a trailing wind. :lol:

John, Bobbie and I generally get about the same as you. But as stated that is with the computer. If you have a GPS, set the mileage to zero when you fill up and check the mileage when you fill the next time. Subtract the beginning from the ending. Divide the miles by the amount of fuel used and you should get your true MPG. At the same time check you miles traveled against the GPS. Also check your speedometer against the GPS to see if your speedo is correct. I have found my speedo to be 5 MPH slower then my actual speed. The GPS is very accurate.

Happy Trails

Herman

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What Herman said. My GPS correction is +5.8% that can add up. My unit doesn’t shift into 6th until 65 mph. I would use at least 10 tanks to get an average that helps average in the conditions you are driving in.

Bill

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My gps and speedometer are the same, I assumed that people were pulling my leg when I heard the type of mileage they were claiming.

Thanks Again

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When I adust my fuel mileage for fuel used by the generator, the Aqua Hot and when idling, my computer is right on.

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Wolfe10

On the mode button is the economy on when the light is on?

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Though it could be programmed either way I am not aware of any RV's that differ from "default to power mode" each time the engine is started.

So, pushing the mode button which turns on the mode light selects for ECONOMY mode.

But, it is quite to verify:

From a stoplight, with mode in the default setting (power mode), accelerate up to 45 MPH at or close to wide open throttle. Note max RPM in each gear.

Press the mode button and repeat. Economy mode should upshift at well lower RPM-- again, ONLY under high throttle positions.

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I use the economy mode and at times i find it's not best to use it. The economy mode is set by pressing the up arrow and then the mode button on my 6 speed. Good to use on flat land but in hilly or mountain grades will hurt speed and fuel mileage. Sometimes it is best for the transmission to downshift sooner.

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Ok so this maybe a dumb question, so it shifts faster at take off, so how does it save fuel at flat cruise control if it still has a 1600rpm at 63mph the motor is still turning the same rpm as in regular mode

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Ok so this maybe a dumb question, so it shifts faster at take off, so how does it save fuel at flat cruise control if it still has a 1600rpm at 63mph the motor is still turning the same rpm as in regular mode

Economy mode makes ZERO difference on flat land cruising. It only makes a difference on places that the throttle goes to or close to WOT.

So, on I 10 in Louisiana, no difference. On I 10 further west in the hill country of Texas substantial difference.

Ray, I am surprised you have to push the up arrow to get the mode button to work. Normally, you can go from power mode to economy mode (and back) by merely pressing the mode button.

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I agree with everything Brett said. Also I believe your tires are rated to 65 MPH. Anything over 65 could spell problems.

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I understand now its more of a in town/ traffic savings

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Are you using any of that BioDiesel added fuel? Biodiesel has much less BTU content than regular diesel fuel. When they add biodiesel to fuel to make it "green", it mostly just adds green to their bank account. You will actually burn more fuel per mile, so any "over all" pollution mitigation or "green" aspects are highly questionable.

I have a CAT turbo 300 and get around 11 MPG towing a Jeep on level ground with no wind in economy mode on the tranny. A lot can be said for large engines and fuel use. That extra power comes with the penalty of reduced fuel economy. Big engines have a lot more "internal friction" and losses than smaller engines and need more fuel just to idle.

Also watch your RPM's, diesels get the best mileage at around 1500-1600 RPM's on the highway. Hills always kill fuel mileage. I never buy fuel with added BioDiesel. Synthetic oil always helps too.

Tire pressure is one of the worst fuel mileage offenders, aside from the headache of more frequent blowouts.

If you smoke at the tailpipe, your wasting fuel. Avoid that as much as possible.

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I am a retired trucker. When I was in the business, I met a driver that worked for a small Caterpillar test fleet out of central Illinois, who showed me fuel mileage records that were astounding. He was running a 550 horse Cat, 10 speed tranny, and usually above 70,000 lbs gross weight. He never got in a hurry, never used his cruise control, and kept his top speed at 55 mph unless on a downgrade. His statement to me was that "you wouldn't want run with me."

We will be leaving for a trip from PA into numerous favorite places in Colorado in August . It will be a lengthy trip and my first time behind the wheel of a diesel motorhome. I traveled the same routes in our 460 Ford powered 34 footer and the fuel mileage was terrible. I was not retired and therefore always in a hurry.

I do know that good advice is to keep your speed down, keep your cruise control off, keep your RPMs down, stay off the accelerator on a slight rise in terrain. Let your speed drop on those slight grades. The amount of time that you lose at the end of the day will really not amount to much, and probably save a lot.

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"Are you using any of that BioDiesel added fuel? Biodiesel has much less BTU content than regular diesel fuel. When they add biodiesel to fuel to make it "green", it mostly just adds green to their bank account. You will actually burn more fuel per mile, so any "over all" pollution mitigation or "green" aspects are highly questionable."

I agree but you won't be going very far. I don't think I have found a station that didn't sell Bio of one level or another. I think if you do a little research you find this is a Federal mandate brought to you by your friendly EPA.

Bill

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ObedB,

Welcome to the forum. Lots of good info but I can't drive 55. Well I have been doing that while in California just to see and it is the speed limit if towing. I haven't done my mileage yet and I may not do to good. I have been running lots of hills like going up to Yosemite on 120 and another road with lots of hills Ca.154. I normally (where I can) drive 65 at 1600 rpm in 6th. At 55 I am running 1600 in 5th. almost always run cruise and econ mode.

Bill

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We just returned from a trip, our first long trip with our 2002 HR Imperial (40PKD) Cummins ISL 400 Allison 3000 6spd. We were towing our Jeep Wrangler which I believe weights around 3300lbs. We had the generator on for 7hrs of the 11 hour trip North on Rt81 from Tennessee. MPG 10.05. I ran the hills at 55 the flats at 62, I tried to accelerate above 62 down hill for the next hill to get a little extra push and I actually stopped to top off the tank, I thought the fuel gauge was broken. We were very happy with the MPG and impressed with the power. :)

At 60mph I was at 1500RPM's seemed a bit high but MPG was better than I expected, compared to our old coach (1998 Coachmen Santara 311SB Class C V10) this journey would have been 6mpg towing with the engine next to me at 4000 rpm most of the time.

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