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Unread 02-17-2014, 07:31 PM   #1
Merkava
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Durango better MPG?

How can a vehicle that's based on Grand Cherokee except it's bigger and heavier get better MPG?
14/20 for HEMI GC
14/23 for HEMI Durango RT

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Unread 02-18-2014, 07:22 AM   #2
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Most likely that's the rating for the 2wd version.
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Unread 02-18-2014, 07:32 AM   #3
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Is that the ratings for the same years? And which years? 2014s?
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Unread 02-18-2014, 08:06 AM   #4
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Does transfer case matter?
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Unread 02-18-2014, 08:35 AM   #5
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http://www.fueleconomy.gov/feg/bymod..._Durango.shtml

http://www.fueleconomy.gov/feg/bymod...Cherokee.shtml

Looks like there is a +2mpg advantage on the highway for 4x4/AWD models. A little could be due to transfer case? The Durango has a lower drag coefficient. That's probably the main reason. They have the same tires, and I believe the same gear ratios. Drag has a lot to do with MPG at highway speeds -- especially when driving heavy beasts.
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Unread 02-18-2014, 09:33 AM   #6
ArloGuthroJeep
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They may have used lighter material. A weaker drive train (due to being AWD instead of 4wd). Lower rolling resistance tires. Could be more aerodynamical (despite being overall bigger).
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Unread 02-18-2014, 09:50 AM   #7
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My hemi durango gets 20 hwy on summer gas. Not 23.
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Unread 02-18-2014, 11:14 AM   #8
chartx
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Quote:
Originally Posted by Merkava View Post
How can a vehicle that's based on Grand Cherokee except it's bigger and heavier get better MPG?
14/20 for HEMI GC
14/23 for HEMI Durango RT
That confusion is around for a while already. The reason is 8 speed vs 6 speed.

20mpg 4WD is for 6 speed hemi, 22mpg is for 8 speed.

When you look at last year's data, 6 speed was 20mpg

http://www.fueleconomy.gov/feg/bymod...Cherokee.shtml

Jeep is also not so keen to clarify this for reasons not so clear.

That new 8 speed is supposedly add 2mpg; see also ram numbers (6 speed vs 8 speed)
https://www.fueleconomy.gov/feg/bymake/Ram2014.shtml

However, I wouldn't trust fueleconomy or jeep listed numbers too much.

They both can be too optimistic as we all know.
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Unread 02-18-2014, 04:57 PM   #9
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I expect these things are rear wheel drive all the time. 4wheel drive when there is slippage enough to get the transfer case excited.
Even Acura MDX with SHAWD is front wheel drive until the rear wheels are called for.
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Unread 02-18-2014, 05:07 PM   #10
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Nah... QTI and Durango are simple old style open light truck transfer cases. Functionally a open diff in the middle and open diffs on each axle (there is just a little rear bias because of the way the gears are designed). They depend entirely on brake traction control to stop wheel spin. These are what some of us call AWD systems. The complexity of axle disconnects (e.g. slip clutches) are added to other more car like vehicles to save some mpg. These are typically not strong enough for light truck applications, light trucks have more significant things that affect mpg. The mpg improvement of an axle disconnect is probably in the noise.

The QTII, on the other hand, has clutches within the transfer case, so it can run in completely open to completely locked depending on the whims of the traction computer. This is a true 4x4 case.
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Unread 02-19-2014, 01:29 AM   #11
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V8 durango uses the same two speed transfer case (mp3022) as the grand cherokees with 4lo. Mp3022.

V6 durangos and grand cherokees use the same one speed transfer case. No4lo
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Unread 02-19-2014, 08:04 AM   #12
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They also have the same tires and gear ratios. Thus, any difference has to be in the drag -- in which the Durango has significantly less of. As stated above, drag make a big difference in a 5200 lb beast in speeds of 65 and above.
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Unread 02-19-2014, 09:35 AM   #13
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The window sticker for a 2014 AWD/4WD Hemi Durango rates the mileage at 14 city / 22 highway. The JGC is 14 city / 20 highway.

It's possible that the drag could be the difference, but I'm not sure.

Real world mileage - I've seen 25 mpg according to the EVIC display going 65 mph on a flat road in my 2014 Hemi JGC.
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Unread 02-19-2014, 09:40 PM   #14
chartx
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Quote:
Originally Posted by hemispin View Post
The window sticker for a 2014 AWD/4WD Hemi Durango rates the mileage at 14 city / 22 highway. The JGC is 14 city / 20 highway.

It's possible that the drag could be the difference, but I'm not sure.

Real world mileage - I've seen 25 mpg according to the EVIC display going 65 mph on a flat road in my 2014 Hemi JGC.
It is puzzling me, last year sticker mpg with 6 speed is still 20mpg highway. Why 8 speed didn't increase the mpg? In ram trucks it did increase 2 mpg on hemi. Same as durango, 8speed increased 2 mpg on sticker.

Most of the time EPA is simply self testing, and occasionally marketing department has a say about it.

By keeping hemi 4wd in 20mpg, the diesel shines even brighter over it. In durango there is no diesel, and in Ram diesel is introduced very recently on 2014 models.
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Unread 02-20-2014, 05:48 AM   #15
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IIRC, manufacturers test their own vehicles (or contract for others to test) for EPA mpg ratings.
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