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Old 05-10-2011, 11:21 PM   #1
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Fuel mileage on 5.9 Cummins

I have a 2000 Discovery Diesel that I recently bought back in So. Carolina. The problem is: It doesn't get the same mileage that I used to get on my 2000 Winnebago Journey that had the same engine. My Winnebago had a 5.9 Cummins also, but was only 36' long. This coach is 37'. I now get 9.0 miles to the gallon where I used to get 11.6 miles to the gallon. It doesn't seem right. I tow the same car that I used to tow (a 2002 Jeep Grand Cherokee) The mileage on the coaches is different. My Winnebago only had 55,000 miles on it where this coach has 85,000 on it. Does this sound kind of funny to anyone else out there?
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Old 05-11-2011, 05:28 AM   #2
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Is there a weight differance??...Are the rims bigger on the new coach.....same transmission??...hmmm
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Old 05-11-2011, 06:39 AM   #3
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And perhaps the gears in the axle are different.

Too many variables are not known too accurately answer the question.
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Old 05-12-2011, 08:25 AM   #4
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There's probably a small weight difference being as the Discovery is a 37' coach and the Journey was a 36' coach. I have not checked exact weights. They both have the same engine and the same transmission. Both had the same tires and rims. As far as rims go, if they were larger on the new coach, wouldn't that improve the mileage? They both are on Freightliner chassis. As far as the rear axle ratio, how do you check that?
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Old 05-12-2011, 09:09 AM   #5
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THe weight could be more than a little different if the vehicle were made in differnet ways with different materials.
And the gearing and Hp ratings may bediffernt as well.
Does this seem to have more power??
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Old 05-12-2011, 09:12 AM   #6
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Actually your 2000 D is 37' 9" long with a base weight of 17,000 lb.

You didn't say what speed you drive at.
The 11 + MPG you got with the last MH was very unusual if it was the 24 Valve ISB.
Usually only some of the older 12 valve 5.9L would attain that.

My Average over 8 years with my ISB is 10.22 MPG speed around 55-65 MPH.
If I keep it at 55-58 average will go to around 10.7 MPG.
Usually pulling a 3,300 lb toad. GCWR around 26,200 lb.

But even when taking long trips without toad I never had one tank to hit in the 11 range. Probably drive a little faster then.

I do know of one D owner with a 2000 says he gets 11.3 MPG.
But non of the other D owners even mention of being in the 11 range.

Anytime you need information with problems on your D.
Try the Discovery Owners but it does cost to join.

My 99 has a 4.63 rear end. Mine is a Meritor RS-17-145 15,500 GAWR and yours is a 17,000??.
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Old 05-12-2011, 09:18 AM   #7
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Quote:
Originally Posted by Ramzfan
There's probably a small weight difference being as the Discovery is a 37' coach and the Journey was a 36' coach. I have not checked exact weights. They both have the same engine and the same transmission. Both had the same tires and rims. As far as rims go, if they were larger on the new coach, wouldn't that improve the mileage? They both are on Freightliner chassis. As far as the rear axle ratio, how do you check that?
Taller rims generally have more weight, rotating mass, and increased rolling resistance. That = more fuel consumption. Granted once your moving they would rotate at a slower pace than a smaller rim. But the increased starting resistance could rob more fuel than the slower revolutions It's a hard fight of acceleration vs top end.

As for the gears, without a tag on the axle or a call to the manufacturer ( I don't know how many choices if any were available), you'll have to lift the rear tires off the ground. You will have to count the difference in revolutions. Ie: one driveshaft revolution could spin the tires 5 times (5:1 rear axle ratio) this alone is a HUGE factoring of fuel efficiency.
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Old 05-13-2011, 10:29 AM   #8
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You didn't mention the HP of either 5.9. Our 38' 2001 Sportscoach with the same chassis and the 275 HP 5.9 gets 11.5 MPG at 65 MPH. We live in Florida on flat land and do not tow anything yet. Maybe other owners of your exact set up will chime in with their MPG. DACOTAH
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Old 05-13-2011, 10:47 AM   #9
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Quote:
Originally Posted by GreaseMonkey View Post
Ie: one driveshaft revolution could spin the tires 5 times (5:1 rear axle ratio) this alone is a HUGE factoring of fuel efficiency.
It's the other way around. A 5.00:1 rear axle ratio requires 5 driveshaft revolutions (pinion gear) to spin the tires (ring gear) 1 revolution.

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Old 05-13-2011, 12:05 PM   #10
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Our 2000, 36' Journey with the 24V, 5.9, 275 Hp, pulling our Ford Explorer, also gets 11.5 in Georgia and Florida.
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