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Old 03-26-2014, 04:33 PM   #1
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2012 ISC Fuel Mileage

I have a 2012 ISC 350/1,000 with all the pollution junk. It is in an M2 chassis with a motorhome box. It is under 20,000 lb. and it gets terrible fuel mileage. Driving in the 65-70 MPH range on flat roads it only got an average 7.4 on a recent 2,000 mile trip.

Is this normal or does anyone have some suggestions?

Thanx
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Old 03-26-2014, 04:45 PM   #2
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Not sure what your total weight is and if you are towing. Mileage sounds in the ballpark. I have the same engine. I've found that slowing down makes a big difference. I drive between 55 - 60, I'm not in a hurry like I used to be.
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Old 03-26-2014, 04:53 PM   #3
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It is under 20,000 lb. and not towing. I've tried slowing down to 65 but after the first few times of almost getting run over by a tractor trailer and looking like a road block, I bump it up to 70MPH to at least keep up with the others in the slow lane.
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Old 03-26-2014, 04:54 PM   #4
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From reading many posts on the subject it seems that 7 to 8 seems to be the standard. Doesn't make any difference if your in a 20k with 350 HP or a 40K with a 500 HP. They all seem to get between 7 and 8 MPG.
I don't take mine, I don't want to know. I'd rather pretend I get 10 MPG even though that is not realistic. As Adam from Myth Busters says "I reject your reality and substitute my own"
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Old 03-26-2014, 05:45 PM   #5
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I never really checked mine before either. I was always pulling a big trailer or using the generator a lot. I have just read too many posts that said similar units were getting 10.I had to check.
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Old 03-26-2014, 06:20 PM   #6
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Quote:
Originally Posted by az99 View Post
It is under 20,000 lb. and not towing. I've tried slowing down to 65 but after the first few times of almost getting run over by a tractor trailer and looking like a road block, I bump it up to 70MPH to at least keep up with the others in the slow lane.
I run 60 MPH and don't worry about what the others are doing. I am well within the speed limits and save on fuel! I have a 380 Cummins and am around 40,000 lbs with toad. Not needing to find a way around the driver in front takes a lot of tension out of a trip. I have done this coast to coast as well as Canada. Do the math .5 gallons per mile saves 50 miles per tank or about 6 gal. @ $4 per gallon that's $24 per 100 gal Tank full! I'll put on about 12,000 miles this year. Yearly saving = $$$$$$$
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Old 03-26-2014, 09:03 PM   #7
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According to a Cummins rep at a rally, 7-8 is normal. In fact, he said if anyone with a Cummins claims 10 or over they are lying.
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Old 03-26-2014, 10:54 PM   #8
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According to a Cummins rep at a rally, 7-8 is normal. In fact, he said if anyone with a Cummins claims 10 or over they are lying.
I'll agree about the lying part. I have seen as low as 2.3 and as high as 99.9 on mine. My average runs mostly in the 8.4 to 8.7 range. I usually run at 1700 RPM My motor is a '01 vintage in an '02 coach.
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Old 03-27-2014, 05:58 AM   #9
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Thanx for all the replies.
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Old 03-27-2014, 06:24 AM   #10
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Originally Posted by Luckiest Dreamer View Post
I run 60 MPH and don't worry about what the others are doing. I am well within the speed limits and save on fuel! I have a 380 Cummins and am around 40,000 lbs with toad. Not needing to find a way around the driver in front takes a lot of tension out of a trip. I have done this coast to coast as well as Canada. Do the math .5 gallons per mile saves 50 miles per tank or about 6 gal. @ $4 per gallon that's $24 per 100 gal Tank full! I'll put on about 12,000 miles this year. Yearly saving = $$$$$$$
But the other side of that is on a 2400 mile trip the .5 MPG increase by dropping from 70 to 60 will save $92 but add 6 hours of drive time.
I personally don't like being out on the highway at any speed. So adding 6 hours of drive time to save $100 is not very appealing. And I am not sure where you drive but I can guarantee you driving 60MPH on 95 or 81 will add far more tension to your trip than going the speed limit and keeping up with the flow of traffic. East coast drivers are all in a hurry to get somewhere.
So the choice is ours. Thanx for your insight.
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Old 03-28-2014, 11:02 PM   #11
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aerodynamics is a big factor, under 20k...not so much
i get 7.5 to 7.7 at 63-64 mph and we pull the truck on a flat bed out back and total weight is just a shade over 39k

i have found it will flat out go through some fuel if i run 67 or higher

1700-1800 rpms seems to be its sweet spot if you will
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Old 03-29-2014, 11:37 PM   #12
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East coast drivers are all in a hurry to get somewhere.
did you imply west coast drivers are NOT in hurry to get somewhere? LOL
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