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Old 05-09-2012, 08:33 AM   #1
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BETTER mpg in 4wd...???

Howdy, all.
I noticed something odd the other day.
I just rolled-over 8000 miles on my '12 Sahara Unlimited.
I fill up about every 5 days.
I typically average about 17.2mpg and naturally it fluxuates a little each way depending on numerous variables.
Monday, it rained. I reach down and slid her into 4-hi (cuz wet streets are pretty much my only chance to use 4wd).
I'm be-bopping around, usual driving habbits, I glance down and see 19.2mpg
What the (heck) !?!?!
The best Ive ever seen is 21.9mpg and that was all highway...all cruise..from one fueling station to another...no stops.
But to go from 17 to 19 just cuz I shifted into 4wd doesnt make much sense to me.
I thought...bad alignment...wet streets will allow the tires to slip more and reduce resistance. But no feathering on the tires means alignment issue is LESS-likely.
Whatcha think?

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Old 05-09-2012, 08:37 AM   #2
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Quote:
Originally Posted by Vroooom View Post
Howdy, all.
I noticed something odd the other day.
I just rolled-over 8000 miles on my '12 Sahara Unlimited.
I fill up about every 5 days.
I typically average about 17.2mpg and naturally it fluxuates a little each way depending on numerous variables.
Monday, it rained. I reach down and slid her into 4-hi (cuz wet streets are pretty much my only chance to use 4wd).
I'm be-bopping around, usual driving habbits, I glance down and see 19.2mpg
What the (heck) !?!?!
The best Ive ever seen is 21.9mpg and that was all highway...all cruise..from one fueling station to another...no stops.
But to go from 17 to 19 just cuz I shifted into 4wd doesnt make much sense to me.
I thought...bad alignment...wet streets will allow the tires to slip more and reduce resistance. But no feathering on the tires means alignment issue is LESS-likely.
Whatcha think?
#1: Must be a coincidence.

#2: Probably not fatal, but not a great idea to drive around all day in 4WD on wet pavement just for the novelty of it. Will unnecessarily stress your driveline and won't really help drivability much.

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Old 05-09-2012, 08:39 AM   #3
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agreed with marine hawk

did you pump the reset button. horrible location for it and way to easy to reset
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Old 05-09-2012, 08:40 AM   #4
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#1: Must be a coincidence.

#2: Probably not fatal, but not a great idea to drive around all day in 4WD on wet pavement just for the novelty of it. Will unnecessarily stress your driveline and won't really help drivability much.
x2, 4WD on wet pavement isn't necessary, it will probably hurt more than it will do good.
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Old 05-09-2012, 08:40 AM   #5
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Rain or wet roads usually hurt MPGs... kind of like walking through a shallow pool. Strange things happen, though. My '11 averages 17-18 MPG around flat Dallas /Ft. Worth but got 21 MPG searching for gears through the Rockies with my foot planted. It was as if the 'ol 3.8 likes being pushed rather than babied...?
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Old 05-09-2012, 08:48 AM   #6
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The computer logarithms are subject to TO MANY VARIABLES--

I read about a guy who got 458.7 mpg in his JK-thats what the dash said-

Takeit to the bank-

Distance traveled/gals used + MPG--figureitout !

JIMBO
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Old 05-09-2012, 09:03 AM   #7
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Quote:
Originally Posted by JIMBOX
The computer logarithms are subject to TO MANY VARIABLES--

I read about a guy who got 458.7 mpg in his JK-thats what the dash said-

Takeit to the bank-

Distance traveled/gals used + MPG--figureitout !

JIMBO
Clearly I can get over 1000 MPGs! Can't we all?? ;-)

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Old 05-09-2012, 09:12 AM   #8
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Reliability of the "Avg Mpg" Computer:
I hand calculate MPG when I fill-up and find it very closely reflects what the computer indicates.

Reset the computer:
I reset everything everytime I refuel...MPG...Timers...Trip A

Cant use 4wd on wet streets.
Cant use 4wd on dry streets.
That leaves....
Ice....dont get much of that in TX
Mud...requires rain...dont get much of that.
Rocks....requires time to go play...dont get much time for that.

Sounds like I shoulda bought a prius.
(yuck) not gonna happen.


Best swag I can come up with is the storm brought a 30kt tail-wind. I musta been looking at the MPG after being pushed by the gusts for a while. (shrug) just interesting.
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Old 05-09-2012, 09:27 AM   #9
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I should also mention that it wasnt an instant or brief indication of 19.1mpg.

It started at 17-something...
I shifted into 4H
It gradually increased to 19-something...
And stayed in the 18.9-19.3 range for about 30 minutes (25-30 miles)
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Old 05-09-2012, 09:29 AM   #10
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thats wierd. i wonder what the actual algorithm is for that and if its a bug
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Old 05-09-2012, 09:38 AM   #11
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dunno... should be a very simple function of
Miles per hour divided by gallons per hour equals miles per Gallon.

Standard fuel burn calculation. nothing tricky.

It is, of course, a calculation of "AVERAGE"

So...if you refuel....get going a good speed...down hill...with a tail-wind...and coast...
your miles per hour will be way up....gallons per hour way down....
Take a snapshot of that scenario (reset computers)
you'll get funky numbers....briefly.
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2005 Black Suzuki C50T (ours)
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Old 05-09-2012, 09:56 AM   #12
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I agree with the Marine. When the Zombies come to TX you might just need 4WD.
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Old 05-09-2012, 10:03 AM   #13
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Indeed.

I'll add that to the list of approved 4wd surfaces:

Ice
Mud
Rocks
Zombies

I wonder if we could get Goodyear to make a Zombie-Terrain tread-design....I'd make it look like interlocking hand-prints....maybe an occasional face-print here and there.
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2012 Black Unlimited Sahara (mine)
2011 Black Corvette 3LT (wife's)
2005 Black Suzuki C50T (ours)
"Hope" is NOT a strategy
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Old 05-09-2012, 10:22 AM   #14
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I wish the jeep had the option of not coming with the stupid mpg calculator. Is there any way to disable it? I always have the urge to check it and it bothers me. Sorry about the hijack.
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Old 05-09-2012, 10:25 AM   #15
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My Subaru I traded in for the Jeep had a MPG gauge, like Uhauls
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Old 05-09-2012, 10:27 AM   #16
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Its all about how you interpret it...

I call it a "Miles Per Grin" indicator.

Should be MPS....Miles Per Smile.

I'd like it to be better fuel economy...duh.
Im glad its nots worse...duh
I'm happy with what I got....duh.
Life is good.


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2012 Black Unlimited Sahara (mine)
2011 Black Corvette 3LT (wife's)
2005 Black Suzuki C50T (ours)
"Hope" is NOT a strategy
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