Seanz2003

Hello,
Sorry if this has been asked before...I'm new here, and to the Jeep world in general, as well as, all the different mods that come with it. My wife surprised me this past Christmas with a 2015 JKU sport. The previous owner had obviously done some modifications, but my wife didn't think to ask the dealer specifically what had been done. I don't know offroad jeep hardware well enough to look at it and recognize lift, suspension, drivetrain mods, etc. But I do know that it has 35" BFGoodrich MTs on 17" inch beadlocks. I am clueless about any gearing or suspension mods. The jeep drives fine on the freeway, and there no engine warning lights illuminated that might suggest a problem. The odometer and speedometer seem to reasonable based upon my driving habits, but I haven't attempted to verify either. The Jeep is my daily driver so I have noticed a significant hit in gas mileage compared to my previous vehicle. The ECU reports that it gets between 11-13mpg (mostly street driving) and 8 or 9 on the trail. That seems pretty awful to me when the stock Jeep should get about 17-20mpg. I am NOT an aggressive driver- usually pretty easy on the gas pedal. I would assume that if it has the proper gearing, it should get something closer to 15-17mpg. That said I have several questions
TLDR;
1) What would be normal or expected mileage for 2015 JKU on 35's? Can someone with 35's clue me in to what they get?
2) How would I go about figuring out exactly what is stock and what is not on (previously-owned) Jeep?

[Edit] ... so after I posted a bunch of fuel mileage related threads pop up down there \/ 😣

karls10jk

They don't get great mileage on 35's and with beadlocks you've got extra weight there that isn't helping your situation. It sounds like your speedometer isn't calibrated though and with it being a 2015, that makes sense. When they came out, superchips was having owners send in their computer in exchange for an unlocked one.

But...to get back to your question, I average 15-17mpg (calibrated) in my 2010 2dr that weighs just shy of 5k lbs. I've got the 3.73's. The pentastar (your engine, 2012+) typically does a mile or two per gallon better. So if your weight is similar to mine then you should be around 16. I also added a high flow air filter which some people agree with and others disagree. It's a daily driver so I need all the help I can get.

It may be worth looking into and reading reviews in Jscan OBD, it's an app that claims to be able to change tire size in the Jeep computer and it's very reasonably priced compared to the competition.

Mark Doiron

What Karl wrote above. To expand a tad further just in case you don't know: The speedometer calibration affects the odometer and all of the readings that are derived off the odometer--including MPG. So, if your speedometer isn't calibrated, you have no way to know what your gas mileage really is unless you have a known driving distance (say, you know it's 3.2 miles to the office, ant that's all you drove this week).

Second, it's misleading to compare gas mileage numbers because Jeep weights are all over the map, altitudes they are run at are all over the map--yes, altitude affects gas mileage--it's a couple MPG better in Colorado than in Oklahoma, for example--you have no idea whether they have an accurate speedometer, or whether they are computing the gas mileage manually or just relying on the MPG meter, you don't know what kind of gas they bought and on and on and on. I say this because some folks say they get in the low 20s regularly, and others are like me and get in the low teens. All over the map. Just get your own speedometer accurate, then track it against your own numbers. And I'd recommend calculating it manually to see how your gauge compares. But don't bother until you have that speedometer calibrated.

One last item: If it turns out your speedometer is already calibrated, then you need to find out how the original owner went about that because generally those programmers are locked to a VIN number. He should give you the programmer--it's no good to anyone else.

jadmt

I have had 4 jk's a 2013 jku with auto and 3.21's, 2014 jkur auto and 4.10's, a 2016 jkr with auto and 4.10's and 2018 jkur auto with 4.10's,. I used a procal on all of them and all speedos and odometers were sport on. On the 2013 sport 1.5" lift and I ran 285/75-16 tires and it got 16-18 mpg hand calculated. on the 2014 I had a 3.5" lift and 35's (toyos on AEV salta rims) and that thing always got better mpg it was common to get 18-20mpg traveling 65-70mph. The 2016 had a 3.5" lift and 35's (same tires and rims as on the 14) and it never got close to the same mpg as the 2014 even tho it was a 2 door. I ran the same bumpers on both as removed the bumpers from my 14 when I sold it. I was lucky to get 14-16mpg travelling the same speeds and routes. My 2018 with 35's gets 15-17mpg and again 35's and lifted. Like was said mpg is all over the place even between same model jeeps. All of my did a lot of miles on the same routes and I check mpg by hand every tank full.

bbolander

My 2012 JKUR has a 2" lift, 34's, auto, 4:10's, heavy bumpers and winch. I have corrected the speedometer with Superchips. I have 50k miles on it and average about 17 mpg very consistently. It often includes 1/2 tank of freeway driving, the rest around town. My Evic typically shows about 1/2 mpg more than the actual.

JKUsport16

I bought a 2016 JKU in January, it already had a lift, 35's tires, after market bumpers, rear swing out tire carrier, winch. I could tell right away that the speedo was off. Done some research which also said the shift points could be off.....started paying attention and sure enough it seemed like it was searching for when to shift in higher gears. Picked up a flash-cal and re-calibrated for 35'' tires which put the shift points back correct. I've only drove back and forth to work (80 miles a day) and get 15.5 to 16 mpg.

3rd Jeep

I have a 2013 JK 2dr with 315 70R 17s (34.6”), automatic with 3.21 gearing. I have both the hard top and a Trektop NX. With the hard top on I average (calibrated) between 15.5 – 16.5 mpg. With the Trektop on, I average 16.5 – 17.5 mpg. Most of my driving is highway during the week with local trips on the weekends. I rarely top 70mph on the highway.

resharp001

There are so many variables for each persons application, but the general, all encompassing answer is "poor". That's ok though.....what you give up in miles, you make up for in smiles. I'm down to 13.5 mpg with current build. Don't care one bit. That's like damn Prius compared to the 5.5 mpg motorhome gets loaded down and towing it!

Seanz2003

Thank you all for info! After reading through the replies as well as other threads, I understand that the fuel economy can be all across the board. I tracked my mileage this week on each trip comparing it against Google maps and it seems the odometer is about .5 miles off for every 5 miles driven. Now I'm wondering if the overall mileage ; instead of 67,000miles it's probably significantly more :/ Some of have mentioned different programmers: JScan, Superchips, Procal. Is one better than other? Do these use the obd2 port? I thought obd was read only.

resharp001

Many people don't bother to program tires up to 35s as it only throws the speedo off by ~5mph at interstate speeds. This obviously effects anything the computer calculates, and importantly the odometer as well. It also affects the shift points on an automatic transmission, but many people just live with it as their new "normal". In regards to programmers, the AEV ProCal is the "ole reliable". It's not fancy, but it gets the job done in simple fashion without much hassle. Anything that has software downloads is going to introduce the possibility for frustration, but doesn't mean they are bad necessarily. I have a Bully Dog. It sux IMO. I've used a newer Superchips F5 and it was a nice intuitive interface. It's not worth the money to buy a more pricey model that can do various "tunes". Simple programmer is all you need.