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Old 03-05-2014, 12:05 AM   #1
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Gas mileage and high speeds

Hey y'all. I have a 2010 JK 2door that I bought second hand with 26k miles on it. I'm just curious about the gas mileage. I know they aren't efficient vehicles, but at my last fill up I calculated that I only got 12.3 MPG. The dash fuel economy readout reflects about the same. Is this normal? It does have larger tires than OEM. I believe they're 255/70R17 instead of something like 225/75R16 I believe. Plus they're BFG Mud Terrains so definitely not the most economical tire. I drive mostly in town, but do travel to the nearest larger city every once in a while which is about 40 miles away.

Also, I've notice that my Jeep feels like it likes to travel on the interstate around 60mph. Any faster and it seems like I really have to press on the gas pretty good. Then, whenever I go up even the slightest overpass it slows the Jeep down a bit and I have to give it the gas to maintain speed. Now I know that when going up a large bridge this is normal for any vehicle, but this Jeep just feels like it has no power. Is this just the way a Jeep drives? This is my first. Honestly, I don't enjoy driving it on the interstate because of this. I feel like I'm almost burning the motor up to maintain speed. It doesn't take much to send it to 4k rpms or more and it's gone into the red a couple times when passing and such. To be honest, I'd rather drive my wife's '08 RAV4 2.4L on the hwy. Feels like it has more power, smh.

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Old 03-05-2014, 12:35 AM   #2
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Those are the virtues of the 3.8L engine. If you want to feel better just realize that everyone of those cool looking high lifted Jeep with 35 and 37" tires is getting worse gas mileage on the road than you are.

Off road it's a different story.

BIGbadJOHN I suggest you reconsider the last sentence in your post before you get some BIGbadFlames. Many of us have felt your frustration.

If you don't know your gear ratio what is you cruising RPM at 60 MPH?

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Old 03-05-2014, 12:54 AM   #3
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Originally Posted by BIGbadJOHN View Post
To be honest, I'd rather drive my wife's '08 RAV4 2.4L on the hwy. Feels like it has more power, smh.
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Old 03-05-2014, 01:12 AM   #4
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Not sure what RPM it runs at exactly, but I'd say somewhere around 2k or so. Not more. I'll have to pay closer attention next time I take it on the interstate. Do I need to adjust the computer to shift more appropriately for the 255's? I wish I would have bought a manual so I wouldn't have to worry about that.

And sorry you guys don't like my last sentence, but it's the God's honest truth. Her little RAV is much better on the hwy and there is no argument to be had there. Different vehicles for different purposes. I just figured the Jeep would be more balanced as far as MPG. I'm sure switching from the BFG MT's to some more appropriate AT's would improve the MPG at least a little as well.

Were the old straight 4.0's as bad on MPG and hwy speeds as the 3.8's? I know I test drove a 2005 manual and it idled smooth as butter and drove like it as well. Too much salt water corrosion on it for my liking though and I passed on it and bought this one a couple hours later.
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Old 03-05-2014, 01:35 AM   #5
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My comment about your last sentence was totally tongue in cheek. You are not the only that has felt that way.

If your RPM is that low you must have low numerically gears. Although that usually leads to better gas mileage. Once you get the gear ratio setup accordingly, the programmers like Superchips help noticeably but don't expect miracles.

You are right about the tires, a less aggressive tread will improve MPG. Look at the gear charts for the 3.8 auto and shoot for the green band of RPM and gear ratio. Keep in mind some of the gear charts are for 70 MPH. You have 31" tires with stock gears so you shouldn't have both poor MPG and performance. Jeeps are not know for the impressive performance but they performance is not that relatively poor.

If you had a manual, you would likely loose the ability use the top gear.
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Old 03-05-2014, 02:02 AM   #6
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I have a 2011 with 33s and a rough country lift which is a manual 6 speed and I feel your pain as far as power goes I run 70 on the interstate but in 6th gear if I hit the slightest hill I'm dropping gears but I'm averaging 14-17 mpg but my rpms stay pretty low I wish I knew the gear ratio I purchased it already set up and has a pretty aggressive tire as you can see

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Old 03-05-2014, 06:53 AM   #7
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Let's go back to your tires. Did you replace the 29" base Sport tires with the Rubicon 32"? If so you absolutely need to recalibrate your speedometer and automatic transmission for proper speed and shift points. A dealer should be able to do that for you or you can get an AEV Procal.
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Old 03-05-2014, 07:18 AM   #8
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Let's go back to your tires. Did you replace the 29" base Sport tires with the Rubicon 32"? If so you absolutely need to recalibrate your speedometer and automatic transmission for proper speed and shift points. A dealer should be able to do that for you or you can get an AEV Procal.
I have the same problem with my 2010 4door as far as mpg
I was wondering if the previous owner programmed the computer for the big wheels

Can a dealer really do this? I always assumed that you had to buy a programmer and do it yourself
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Old 03-05-2014, 08:56 AM   #9
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I have an 07' 3.8 JKU with 285/70/17 BFG ATs. Not too much bigger than stock and a 2.5" lift. I try to keep it right at 70 on the highway and I never re-calibrated so I'm not sure how accurate this is, but here is a pic from last night. I think a lot has to do on how you work the gas.
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Old 03-05-2014, 09:01 AM   #10
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I have an 07' 3.8 JKU with 285/70/17 BFG ATs. Not too much bigger than stock and a 2.5" lift. I try to keep it right at 70 on the highway and I never re-calibrated so I'm not sure how accurate this is, but here is a pic from last night. I think a lot has to do on how you work the gas.
I just like seeing the 93,000 miles on your rig, what if any repairs have you had? Tire Life? Brakes Life? Etc?
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Old 03-05-2014, 09:16 AM   #11
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This may a bit off topic, but just a little bit.

Monday morning I was working in the garage when my store clerk called out that someone drove off with the gas hose from one of my pumps. I ran out to my Jeep and jumped on the interstate to catch this moron. Now my Rubicon will do 100 m.p.h. and no faster. That's how fast I was traveling to get my hose back.

As I was cruising down the highway at 100, I was watching the mpg indicator on my Jeep ticking backwards from 16.6 mpg to 13.8 mpg in just 14 miles of driving that fast. I always knew that higher speeds were bad for economy, but I never knew it would do that so fast.

I got my hose back. The driver was a 62 y.o. cross dresser that was moving to Albuquerque. He was 6'2", balding and no way could he pass as a woman and he tried crying to gain sympathy and keep me from calling the cops. It didn't work. It wouldn't work if it was a female that was 28 and beautiful, why would it work with a guy in a dress?

I need to sell this place.
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Old 03-05-2014, 09:54 AM   #12
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This may a bit off topic, but just a little bit. Monday morning I was working in the garage when my store clerk called out that someone drove off with the gas hose from one of my pumps. I ran out to my Jeep and jumped on the interstate to catch this moron. Now my Rubicon will do 100 m.p.h. and no faster. That's how fast I was traveling to get my hose back. As I was cruising down the highway at 100, I was watching the mpg indicator on my Jeep ticking backwards from 16.6 mpg to 13.8 mpg in just 14 miles of driving that fast. I always knew that higher speeds were bad for economy, but I never knew it would do that so fast. I got my hose back. The driver was a 62 y.o. cross dresser that was moving to Albuquerque. He was 6'2", balding and no way could he pass as a woman and he tried crying to gain sympathy and keep me from calling the cops. It didn't work. It wouldn't work if it was a female that was 28 and beautiful, why would it work with a guy in a dress? I need to sell this place.
Even though I feel bad your property was damaged... I love reading/hearing of stories like this.
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Old 03-05-2014, 10:15 AM   #13
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Originally Posted by PecosRiver View Post
This may a bit off topic, but just a little bit.

Monday morning I was working in the garage when my store clerk called out that someone drove off with the gas hose from one of my pumps. I ran out to my Jeep and jumped on the interstate to catch this moron. Now my Rubicon will do 100 m.p.h. and no faster. That's how fast I was traveling to get my hose back.

As I was cruising down the highway at 100, I was watching the mpg indicator on my Jeep ticking backwards from 16.6 mpg to 13.8 mpg in just 14 miles of driving that fast. I always knew that higher speeds were bad for economy, but I never knew it would do that so fast.

I got my hose back. The driver was a 62 y.o. cross dresser that was moving to Albuquerque. He was 6'2", balding and no way could he pass as a woman and he tried crying to gain sympathy and keep me from calling the cops. It didn't work. It wouldn't work if it was a female that was 28 and beautiful, why would it work with a guy in a dress?

I need to sell this place.
Um, a "cross dressing, hose stealer".
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Old 03-05-2014, 10:30 AM   #14
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That Dude is a real Hoser!!
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Old 03-05-2014, 10:40 AM   #15
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I swear, this place generates the weird and unbelievable.
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Old 03-05-2014, 12:18 PM   #16
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Was it just this guy's "time of the month", and he simply forgot to take the hose out before driving away?
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Old 03-05-2014, 01:01 PM   #17
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Originally Posted by PecosRiver View Post
This may a bit off topic, but just a little bit.

Monday morning I was working in the garage when my store clerk called out that someone drove off with the gas hose from one of my pumps. I ran out to my Jeep and jumped on the interstate to catch this moron. Now my Rubicon will do 100 m.p.h. and no faster. That's how fast I was traveling to get my hose back.

As I was cruising down the highway at 100, I was watching the mpg indicator on my Jeep ticking backwards from 16.6 mpg to 13.8 mpg in just 14 miles of driving that fast. I always knew that higher speeds were bad for economy, but I never knew it would do that so fast.

I got my hose back. The driver was a 62 y.o. cross dresser that was moving to Albuquerque. He was 6'2", balding and no way could he pass as a woman and he tried crying to gain sympathy and keep me from calling the cops. It didn't work. It wouldn't work if it was a female that was 28 and beautiful, why would it work with a guy in a dress?

I need to sell this place.
I am going to go ahead and say your Monday was more interesting than mine.
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Old 03-05-2014, 02:34 PM   #18
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Do you know what your axle ratio is? Most complaints with the 3.8 are a result of 3.21 gears with an auto trans.
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Old 03-05-2014, 03:38 PM   #19
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I just like seeing the 93,000 miles on your rig, what if any repairs have you had? Tire Life? Brakes Life? Etc?
This is my second set of tires. The originals and the BFG's I have now. I have replaced the breaks twice on the front and back. Thats about it with regular maintenance. I do have a very tiny oil leak that started a couple of months ago. I can't really tell where it's coming from yet. When I figure it out I will fix it.
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Old 03-05-2014, 03:39 PM   #20
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Do you know what your axle ratio is? Most complaints with the 3.8 are a result of 3.21 gears with an auto trans.
I have an Auto with 4.10 gears
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Old 03-05-2014, 03:46 PM   #21
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I have the same problem with my 2010 4door as far as mpg
I was wondering if the previous owner programmed the computer for the big wheels

Can a dealer really do this? I always assumed that you had to buy a programmer and do it yourself
A dealer can do it up to 33" tires. You can tell by comparing your speedometer against a GPS.
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Old 03-05-2014, 11:55 PM   #22
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How do I find out what gear ratio I have? I figured all Sport models came with the same gearing. I drove a buddy's 2011 Sport today and the throttle seemed much more responsive on it. I didn't get to take it on the interstate, but the little I did drive it seemed like it had more power or at least more responsive and quicker acceleration. He also has 255R17's on his but more of a street AT tire. His tires also looked much wider than mine even though they were the same size. I didn't get that.

Anyways, seeing Ajax's pic of 17MPG on his dash makes me upset, LOL. Which reminds me that when I drove my buddy's tonight, his average was 16 or so and I know he drives mostly city. Something has to be able to be fixed here. This is unacceptable and sad that I'm getting such poor performance and gas mileage from my Jeep. I've been driving for almost 15 years now and I've driven a few different vehicles and this Jeep has been the most sluggish and, by far, the worst as far as MPG. If I could get it up to 16MPG I would be thrilled. As well as if I could solve the sluggish interstate driving. There's no reason this vehicle should be almost redlining when I give it a little gas. I'm very hopeful that I just need to reset the computer for these tires. I have no engine codes. I got one shortly after I bought it because I took it muddin and a metal T post busted the evap canister. That's been fixed.

It's possible that there were larger tires on my Jeep because when I bought it the salesman said that the man who traded it in wanted his black custom rims and tires back and so they threw on the stock 17's. Would it be very expensive for me to have the dealer reprogram the computer for the size I have?

I truly hope that I can solve the problem of this sluggish performance, because if not I believe I'll be trading it in when I get the chance.
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Old 03-06-2014, 02:09 AM   #23
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2014 Rubi 2 door Auto...I took this when I left Mt Rushmore. It was all down hill and no faster than 50mph... Best mileage ever!!
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Old 03-06-2014, 06:38 AM   #24
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Attachment 839977

2014 Rubi 2 door Auto...I took this when I left Mt Rushmore. It was all down hill and no faster than 50mph... Best mileage ever!!
I have seen as high as 235MPG I have a hard time trusting those stupid AVG/ECO readouts ??????
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Old 03-06-2014, 07:06 AM   #25
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How do I find out what gear ratio I have?
Click on the link below and then "Equipment Listing" on the left side of that page. Type in your VIN and it will instantly give you a pdf copy of the build sheet for your Jeep, which includes the axle ratio.

Online Build Sheet

You can use it to get a copy of any Chrysler vehicle that was built after 1997, so if you have other Chrysler products in the family go for it.
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Old 03-06-2014, 08:38 AM   #26
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It's possible that there were larger tires on my Jeep because when I bought it the salesman said that the man who traded it in wanted his black custom rims and tires back and so they threw on the stock 17's.
I'm no expert and compared to some of the guys on this site I have no idea what I'm doing, but this may be you issue right here. Worth getting checked out IMO.
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Old 03-06-2014, 09:42 AM   #27
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Click on the link below and then "Equipment Listing" on the left side of that page. Type in your VIN and it will instantly give you a pdf copy of the build sheet for your Jeep, which includes the axle ratio. Online Build Sheet You can use it to get a copy of any Chrysler vehicle that was built after 1997, so if you have other Chrysler products in the family go for it.
Apparently my jeep doesn't exist O_O
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Old 03-06-2014, 10:07 AM   #28
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Yesterday I drove from Scottsdale AZ to Farmington NM. Between Scottsdale & Winslow, I got 17 mpg, most of it up hill with speeds from 40-65. From Winslow to AZ/NM boarder, I set the cruise at 75, the computer said I did 16.7mpg, then I slowed to about 68 mph to Gallup, the computer was up to 17.3 at that point. From Gallup to Farmington, I did about 60mph and at fill up the computer showed 19.5 & it calculated to 19.7 mpg.
So higher speeds will hurt you gas mileage.
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Old 03-06-2014, 10:41 PM   #29
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I checked the chart and it came with a 3.73 rear axle ratio. So not the 3.21. I really hope this is just some computer calibration issue. I don't know what else it could be, but I'm definitely not happy with 12mpg. I think something is off to be causing such poor economy. What causes me worry is, like was said, I am getting both poor economy and poor performance. No codes have been thrown though so I have no idea what could be the problem.
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Old 03-06-2014, 11:23 PM   #30
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I just sold a 2010 JKU so mine was a bit different but here are a few things that helped me average around 18 MPG with that Rubi.

1. Tire pressure. I kept it within 5lbs of max when there was not bad weather. Because mine was a daily driver more than off road I had some very nice Michelin all weather tires on there that helped with the mileage.
2. The 3.8L engine in my 2010 really liked the colt air intake from K&N. Yours may not like it so much.
3. Changed out the factory spark plugs for NGK Iridium.

I hope this helps.

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