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Old 05-09-2022, 11:25 AM   #1
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Is there a MPG magic bullet?

Welcome to this rabbit hole. So is it a fools errand to try an get better fuel economy whilst not trying to add power? I have a 2000 Dutchstar with an 8.3L Cummins isl. I'm not "overly" worried about mpg, cause I understand big girls gotta eat. But 6 to 7 mpg I think is terrible. And at $5.29 a gal, she's getting just downright hurtful to drive. Are there any products any of you have tried that actually do allow for better economy? I'd like to get 10mpg or more, without sacrificing the power that it does have already.
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Old 05-09-2022, 11:30 AM   #2
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With our ISC there was a significant mileage difference between 90 kmh and 100 kmh. What speed are you travelling at?
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Old 05-09-2022, 11:30 AM   #3
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JMHO: 10 mpg out of your coach isn't going to happen .

My absolute best tankful was 9.5 , overall most trips just barely over 8 .

Here's some reading from Cummins .
Attached Files
File Type: pdf cummins_secrets_of_better_fuel_economy.pdf (964.6 KB, 28 views)
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Old 05-09-2022, 11:34 AM   #4
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Agree, 6-7 MPG with your coach CAN be improved.


Drive in ECONOMY MODE


Slow down-- anything over 60 MPH really hurts MPG


Anticipate= coast rather than accelerate directly to braking.


Don't drive with exhaust brake on all the time, as that eliminates coasting.


You should easily be able to achieve a 10-15% increase in MPG.
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Old 05-09-2022, 11:41 AM   #5
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There are only 3 scientifically proven ways to improve your milage.
1. only drive when the wind is at your back.
2. only drive downhill.
3. tape a raw egg to the top of the gas pedal.

Note; the third one is still under investigation and testing.......

Thank the Lord I dumped my diesel for a gasser.
And it STILL hurts to fill her up.

Mike in Colorado
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Old 05-09-2022, 11:44 AM   #6
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Slow down and watch your RPM to maintain the "sweet spot". Or the alternative is to just park it.

Ken
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Old 05-09-2022, 11:49 AM   #7
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Quote:
Originally Posted by Flyer15015 View Post
There are only 3 scientifically proven ways to improve your milage.
1. only drive when the wind is at your back.
2. only drive downhill.
3. tape a raw egg to the top of the gas pedal.

Note; the third one is still under investigation and testing.......

Thank the Lord I dumped my diesel for a gasser.
And it STILL hurts to fill her up.

Mike in Colorado
We are already seeing lots of RV’s on the road here in BC but I think a lot are camping closer to home. We have been out a bunch of times this year and there are definitely people out camping.

This is the year we chose to catch up on family visits and touring over 6 provinces. We have 11000 kilometres to cover over 8 or 10 weeks. Glad we switched to an electric tow vehicle this year. Shouldn’t be too bad. And some of it will be driveway camping when visiting.
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Old 05-09-2022, 12:08 PM   #8
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I think in the real world getting 10 mpg in a DP is going to be tough.
I have an M11 powered coach and average 7.5. I actually think there's a little room for improvement on that, and feel like my average will be around 8. My early driving habits are hurting my overall mileage number.
So far, I'm not towing anything. I did have a trip where I got almost 9, but also had trips that were closer to 6. These changes were directly related to faster, more aggressive driving, vs more mellow driving. My coach has enough engine to easily keep up with traffic on the interstate going 75. But there is a cost for doing that.

The magic bullet is to just drive slower. I've kept track of my mileage on a spread sheet including driving habits (speed, gen use, AC use) and general conditions (windy, hilly, hot etc) and really the absolute biggest factor is driving fast.
Drive at a speed that gives the peak torque RPM in high gear, and that is as good as it gets. For me, that's around 60-62 on the highway.
Use of economy mode on Allison trannys helps keep the RPM's in that range.
I never used to use it, but I started trying it out, and in my coach it seems to be fine. In my coach, it's worth a quarter to half a MPG. Doesn't seem like much, but that would get me 100 more miles per tank.
Some folks complain it lugs the engine too hard before downshifting. Just watch your temps and manually shift on big climbs if needed.
I sometimes run the genny going down the road. This of course will eat up some of your MPG. I've kept track of this, and factor in the rated fuel burn. 1 GPH for both AC units, 1/2 GPH for one unit. Not exact, but close enough. If you're on the road all day (8 hrs) that could be the same as driving 60 more miles or so. Less gen use, is more mileage.
Consider hauling less stuff. This is not going to give you as much MPG increase as just driving slower, but every little bit helps.

Staying on the interstate seems better for MPG. Less starting and stopping, grades aren't as steep. Slowing down to 30 for every little town, and speeding back up is a MPG killer.

I know a lot of folks will poo-poo the idea of driving 60 on the interstate. I don't sweat it. When I'm in the coach, I'm on vacation, and not in any hurry. I stay in the right lane, and take my time.

While it's not a MPG thing, it's a cost thing. Plan out your trip, and plan your fuel stops at the stations with the best prices.
I see some folks say they just fuel when they get to half, or whatever, but a little planning can save significant money.
Example, for me, going to SoCal means fueling in AZ, probably at a Maverik near the border, and never buying fuel in CA. I have a big enough tank to go 800 or more if I have to, so I can get in, and get out without paying their prices, and their taxes. On a trip like that, I'd probably fuel twice on the way out, (a real fueling, and a border top off) and the way back just to take advantage of lower priced fuel. While I could actually make it to SoCal from my home base without fueling, it would mean buying fuel in CA, and that's a big nope.

And yes, fuel is killing some of us. But from my fuel bill, I'd have to deduct the cost of gas for my SUV, plus X number of days at a motel, since that money is getting spent one way or another. Hotels/motels have gone up, as has gas. Also traveling with dogs, and everyone is charging extra for them now. Saving some additional money since some of my meals are my food in the coach, where in the SUV, it's all restaurant food.
In my mind the cost of a car vaca, vs the RV, the RV is more, but not lots more considering what the SUV style trip would be.

The last consideration is time. In my above comments, I said to drive slower, but the coaches ability to keep going with fewer fuel stops actually gets me there in about the same amount of time despite not driving at the full interstate speed. The SUV will need more fuel stops, more motel days, and motels are time wasters. Check in, unpack, eat, pack, check out...
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Old 05-10-2022, 12:16 PM   #9
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Ive got a Cummins Big Block (ISX15) pulling around a combined weight of RV and towd of more than 42,000 lbs. Except when I'm climbing out of Phoenix I almost always can achieve 7 mpgs or better. I dont really drive for mileage and usually set the cruise at about 72 when on the interstate. I agree, I could probably achieve slightly better mileage if I slow down a bit. But be careful not to go too slow and below your engine's sweet spot, causing the engine to lug or even down shift. For me, that's about 1400-1500 rpms and about 68 mph. With my 13 speed Eaton, it shifts into 13 gear at about 63 mph. On my upcoming 5,000 trip maybe I'll give it a try and see if my mpg average improves noticeably. If I improve my mileage by just 1/2 an mpg, I will save $250 over the 5,000 miles. That's only $50 a week over my planned 5 week trip. Not exactly a lot of money to really get excited about.
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Old 05-10-2022, 12:27 PM   #10
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No, there's nothing you can do. There are a lot of anecdotes, rules of thumb and old wives tales out there about fuel economy. Once you've done all the obvious, inflate the tires, keep her tuned, don't drag race, there's nothing left. No magic bullet, no secret sauce. She'll get what she gets.
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Old 05-10-2022, 12:50 PM   #11
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Those of us who were around at the time learned learned the 'magic bullet' back in the '70s when the speed limit changed to 55 mph.
If you want noticeably better gas mileage then you've got to slow down.
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Old 05-10-2022, 04:09 PM   #12
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So... all things considered equal will I get better mileage at max torque rpm, max hp rpm, or somewhere in between?
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Old 05-10-2022, 04:16 PM   #13
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Quote:
Originally Posted by Podivin View Post
Those of us who were around at the time learned learned the 'magic bullet' back in the '70s when the speed limit changed to 55 mph.
If you want noticeably better gas mileage then you've got to slow down.

Except we had a Volvo that hated 55 mph. We were way off the torque peak for the engine and we were not in a fuel-efficient range. We got much better fuel economy between 70 and 75 mph.

So slower speed is not the answer unless the vehicle was optimized for the lower speeds.

Ken
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Old 05-10-2022, 04:25 PM   #14
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So... all things considered equal will I get better mileage at max torque rpm, max hp rpm, or somewhere in between?

Yes
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