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Old 11-17-2017, 01:40 PM   #1
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Progress on Diesel engine efficiency in MPG?

What, if any, advancement has been made in diesel engine efficiency in mpg in the past 15 - 20 years as it relates to MH's? In the interest in trying to keep an "apples to apples" comparison, let's consider a 40' DP in the 28k to 32k lb range? I realize that there are many exogenous variables such as % grade, wind, etc., so let's consider relative mpg over, say, a 10,000 mile run. I don't keep accurate mpg figures, but I estimate that my '04 DS averaged 7.5 mpg over an 8k trip with about 20% mountain driving. If I had a nice, new 40' DP, would I see a noticeable increase in mpg?

Thanks for your input.
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Old 11-17-2017, 01:44 PM   #2
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My 33' Fred gets 9 to 9.5 over a 2 year period.
For sure your bank account would go down faster.
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Old 11-17-2017, 01:52 PM   #3
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We had an '11 Journey 40L with a 2007 complaint 8.3/360 HP Cummins 75,000 miles towing a 5500 lb pickup and got 6.8 MPG with a pencil and paper. 7 cross country and 7 MA to FL trips, FL trips had a golf cart in the pickup.
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Old 11-17-2017, 02:29 PM   #4
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I honestly think the Fuel economy has gone backwards instead of forwards. My 1993 DP had the cumin's c motor and I got a constant 10.5 towing my little HHR and as much as 11.5 when not towing. I traveled the roads at the speed limit much of the time. Now I am hearing 1- 1.5 mpg less on the same weight coach. To my little pee brain it does not seem like the air is cleaned to the point that offsetsthe loss of MPG and the use of Def. Maybe I am wrong.
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Old 11-17-2017, 04:08 PM   #5
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Blackjack, you are diffidently wrong on the air pollution aspect of the newer diesel engines. I saw a chart recently comparing the pollution of a 1999 engine vs a 2007 EPA compliant engine vs a 2011 EPA compliant engine. I don't remember the actual numbers but the 07 engine polluted like 60% less and the 11 engine was like 99% less.

The 07 EPA engine had a lot of restriction on the exhaust thus for equal size rigs a pre 07 would get much better mpgs. The 11 EPA loosened up the exhaust and the mpgs did go up to nearly as good as the pre 07 engines. Plus the newer engines are producing more torque and horsepower "cleanly"
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Old 11-17-2017, 04:30 PM   #6
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To me it sounds like you are fishing for reasons to upgrade. Just go for it, if you try to rationalize your only fooling yourself, it'll never pencil out.
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Old 11-17-2017, 04:31 PM   #7
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Isn't most of that down to the Diesel Exhaust Fluid (DEF)?

Our supervisor over at the school bus barn was saying something about the requirement being reversed, since DEF itself was apparently a toxic or a pollutant.
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Old 11-17-2017, 04:42 PM   #8
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http://www.discoverdef.com/def-overview/faq/
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Old 11-17-2017, 05:15 PM   #9
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My 2005 Monaco Diplomat 37' at 32K pounds and a 400 ISL (chipped with aftermarket engine fan) was a rocket and got 9.2mpg going coast to coast towing a Chevrolet Silverado. It had a lifetime average of 8.8mpg over 77K.

My 2014 Newmar Dutch Star 40' with tag axle, 37K pounds with a 450 ISL is averaging 7.3mpg. It's suppose to be a more efficient engine. It may burn the fuel with DEF more efficiently, but certainly doesn't run like 05 ISL.

In fairness, the Dutch Star is a foot taller (more front surface area), 5K heavier and dragging another axle. But, I did expect it to get in the low 8's, but no such luck.
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Old 11-17-2017, 06:08 PM   #10
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Progress on diesel engine efficiency in mpg?

My 09 rig with tag and Wrangler is 43,000 with a 425 Cummins. No DEF, with DPF.
This is as close to 10hp per 1000 lbs as you can get! THAT is what needs to be measured and compared.
It gets 7mpg. The mathematical delta on 7 vs 6 or 8 is chump change across 10K + miles annually.
I'm incredibly happy
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Old 11-18-2017, 02:19 PM   #11
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Quote:
Originally Posted by miniceptor86 View Post
To me it sounds like you are fishing for reasons to upgrade. Just go for it, if you try to rationalize your only fooling yourself, it'll never pencil out.
No, wasn't pondering an upgrade - I haven't squeezed the Buffalo sufficiently on our current rig. But I must say you are putting a dangerous idea in my head. :-)
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Old 11-18-2017, 04:43 PM   #12
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Quote:
Originally Posted by ArgoPilot View Post
Isn't most of that down to the Diesel Exhaust Fluid (DEF)?

Our supervisor over at the school bus barn was saying something about the requirement being reversed, since DEF itself was apparently a toxic or a pollutant.
Engines with DEF get better MPG than those without.

The best way to improve MPG is to slow down. I was reading a post on another forum where an RV owner was complaining about his MPG. When asked his speed he said, "between 75 - 80." There's your answer.
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Old 11-18-2017, 05:20 PM   #13
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Quote:
Originally Posted by Cat320 View Post
Engines with DEF get better MPG than those without.

The best way to improve MPG is to slow down. I was reading a post on another forum where an RV owner was complaining about his MPG. When asked his speed he said, "between 75 - 80." There's your answer.


The biggest negative to diesel mpg is the EGR system which started being incorporated in diesels in around ‘03. The EGR systems are also a point of failure in diesels. The DEF systems address the same NOX pollutant as the EGR systems and the incorporation of DEF made it possible to back off on the EGR system somewhat. That improved mpg.
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Old 11-18-2017, 09:09 PM   #14
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Never owned a DP (YET).... I would think something that might be a advantage for a older coach is they might not have as much frontal area for wind drag. Not as tall or wide and also not as much weight to move around thus better fuel economy.

I know with my last gas coach, similar fuel economy (08 vs 97 vs 85) however 4-10ft longer, +/- 2 ft higher and a bunch more weight.

My x inlaws would get approx 8mog on their 09 40ft Discovery

The smaller 33-35ft DP like their excursion frommjust a few years ago some state 10-12+ mpg. However it’s shorter, lighter and lower vs most other coaches.
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