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 Post subject: Mileage Tracking Milestone & MPG Imrpvoement w/o Skids
PostPosted: Tue Apr 03, 2012 11:44 am 
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Location: Midway, Utah
My 2005 Liberty has about 106,000 miles on the odometer right now. As of the last tank of gas I put into her, I have tracked the fuel economy for 100,000 of them (100,299.9 to be precise). Gas prices began to skyrocket shortly after we purchased the rig new in January 2005, so I began tracking the dollars spent and MPGs at each fill up. Being an accounting/finance professional it made sense to put the numbers into Excel and see what the data would tell me over time that might help us manage through the financial pain of rising fuel costs. It also helped give me some basis for some articles I wrote about high oil prices over at The Truth About Cars.

For the record, my Liberty came with Jeep's Off-Road Group package, which included skids (engine, transmission, drive shaft, and gas tank), tow hooks, Goodyear SR-A P235/70R16 tires, and a 4.10 rear end. At 60,900 miles I changed tires to slightly bigger 245/70R16 Firestone Destination A/Ts. (I did not have the odometer reprogrammed for these tires that have a 2.1% larger circumference, but I controlled for it in the math.)

We took three road trips of exceeding 3,000 miles each as well as several shorter trips that had tanks that were predominantly driven on the highway. I tracked those miles separately. Also, at each fill up I indicated whether I thought I used the A/C more than 50% of the time so I could get breakouts with and without the a/c running.

So this is what the Excel pivot tables tell me:

Miles driven:
- City, no A/C: 48,527
- City, with A/C: 32,303
- Highway: 13,591
- Mixed: 5,620 (this category was for fill ups where the miles driven weren't predominantly City, Highway, or Off-road)
- Off-road: 260

Expenses:
- Total spent on fuel: $16,351
- Avg. PPG (price per gallon): $2.67
- Least expensive PPG: $1.45 (12/13/2008)
- Most expensive PPG: $3.96 (7/9/2008)

Gallons:
- Total: 6,196
- Average per fill up: 17.115
- Maximum fill up: 20.652

Gas mileage:
- City, no A/C: 16.4
- City, with A/C: 15.4 (running the A/C cost 0.95 MPGs)
- Highway: 18.9
- Mixed: 17.3
- Off-road: 14.9 (fire roads in Utah, not rock crawling)
- Total MPG: 16.47
- Best mileage on a tank of gas: 22.15 (5/27/2005 while driving from Houston to Dallas with family of 4 and luggage - must have caught a tail wind off the gulf)
- Worst mileage on a tank of gas: 11.67 (8/10/2006)


One final note: while I was replacing my front drive shaft CV joint I removed all of the skid plates except the gas tank skid. In the 8 tanks of gas since doing so I have averaged 17.91 MPG in city driving, an improvement of 1.66 MPG or 10.2%. I think I'll leave them off until gas prices come back down.

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William C Montgomery
The Truth About Cars
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'05 Sport 4X4, 3.7L - Black | Frankenlift II Premium, JBA KJ Lifted A-Arms 4.5 | Cooper Discoverer A/T3 - LT245/75R16, Load C


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 Post subject: Re: Mileage Tracking Milestone & MPG Imrpvoement w/o Skids
PostPosted: Tue Apr 03, 2012 6:09 pm 
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I can tell you that if you 100% if you have the 3.7 V6 you do not have 4.10 gears unless you had them installed yourself.The only KJ's to ever come with 4.10's from the factory are the 2.4 gas KJ's and the 2.5 export CRD's and that is it.

So your mpg's are skewed and you are loosing mpg's from the bigger tires and stock 3.73 gears.


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 Post subject: Re: Mileage Tracking Milestone & MPG Imrpvoement w/o Skids
PostPosted: Wed Apr 04, 2012 11:07 am 
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I did not have 4.10 gears installed myself. My '05 Liberty Sport included the optional factory installed Off-Road Package. At the time (2004/05) Jeep's site indicated the Off-Road Package included a 4.10 axle ratio. That might have been incorrect.

Nonetheless, I wouldn't consider my results skewed. They are accurate for any (mostly) stock '05 Liberty with the Off-Road Package.

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William C Montgomery
The Truth About Cars
The Truth About Guns
'05 Sport 4X4, 3.7L - Black | Frankenlift II Premium, JBA KJ Lifted A-Arms 4.5 | Cooper Discoverer A/T3 - LT245/75R16, Load C


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 Post subject: Re: Mileage Tracking Milestone & MPG Imrpvoement w/o Skids
PostPosted: Wed Apr 04, 2012 10:42 pm 
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Black_Dog wrote:
I did not have 4.10 gears installed myself. My '05 Liberty Sport included the optional factory installed Off-Road Package. At the time (2004/05) Jeep's site indicated the Off-Road Package included a 4.10 axle ratio. That might have been incorrect.

Nonetheless, I wouldn't consider my results skewed. They are accurate for any (mostly) stock '05 Liberty with the Off-Road Package.

Again you do not have 4.10's,only 4 cylinder KJ's have them from the factory.What's going to be skewed by your mpg's is the fact your factoring in the larger tires to a most likely incorrect odo reading due to the gear ratio you think you have to what you really have.


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 Post subject: Re: Mileage Tracking Milestone & MPG Imrpvoement w/o Skids
PostPosted: Thu Apr 05, 2012 9:43 am 
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It doesn't matter what gears I thought my Liberty has. What matters is what gears and tire size Jeep though the rig had when they set the instrument panel calibration at the factory. Since the Off-Road Package was factory-installed, it's a pretty good guess that they got it right.

I've confirmed that they did. The speedometer checks out with the MPH reported on my GPS and with the GPS apps on several smart phones I've owned. It has also checked out with most radar traps I've passed.

And I validated the odometer before and after I went with larger tires. Since the tire circumference was only 2% larger I was not required to have a Jeep dealership recalibrate my instrument panel (the State of Texas only requires this if tire circumference varies more than 5% from stock).

My mpg math was simple: number of miles driven according to my tripometer, which I reset after every fill-up, divided by the number of gallons required to fill the tank. After I changed to tires with 2.1% greater circumference, I corrected for that difference since the odometer hadn't been updated to reflect that change. What I thought the axle ratio to be was not part of the math.

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William C Montgomery
The Truth About Cars
The Truth About Guns
'05 Sport 4X4, 3.7L - Black | Frankenlift II Premium, JBA KJ Lifted A-Arms 4.5 | Cooper Discoverer A/T3 - LT245/75R16, Load C


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