3.6 Trash MPG

[MEski4x4]

Hey guys - it's been a while but I am finally back in a JLUR and I'm having some issues with absolute trash fuel economy. My daily driving is 30mph or less for maybe a combined 3 miles so I'm not expecting anything great. Currently sitting around 13mpg (was around 10 with leaving it running during the winter). Did a roadtrip to my house up in Maine a few weeks ago, and the Lie-o-meter was 14.6 on the way (but there was a 30mph cross/headwind) and on the way home I squeaked out 15.6mpg. On the trip up, I went through 3/4 of a full tank of 87. Cruise control was set at 70 (which is actually 73) the whole time on the interstate, and up north was 10min trips at 35-55. Transmission had no problems hitting 8th and really never had to drop below 7th except for the occasional monster hill. The only thing to mention (mods below) is I have not adjusted my speedo for the tire height (but I've done the math).

2020 JLUR Hard Top
44k miles
3.6 Pentastar w/8spd
35" Duratracs @ 37PSI
PSC Bruiser Stubby with Warn Zeon 8-S
Factory rear steel bumper
No lift. No engine mods.

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[Shibadog]

Is that hand calculated or dash readout? The 35’s aren’t helping you, but that’s pretty poor mileage. Start /stop commuting is the worst, and if you tend to hit the loud pedal hard when leaving a stop that’ll suck fuel as well. I’d try babying it with nice gentle acceleration, coast down to stops, etc. and see what happens. If you’re still getting lousy mileage something’s screwy.

 

[jludave]

The only thing to mention (mods below) is I have not adjusted my speedo for the tire height

You should use a programmer to adjust and then report back.

 

[MEski4x4]

That's dashboard MPG - but I know it isn't much better than that. The trip north was 172mi and with 2 stops and no mashing of the go-pedal, I burned fairly close to 3/4 of a tank. The way home was just about 1/2 a tank. I've always driven fairly conservatively (coast to stops, don't tailgate/constantly brake) and even getting on the highway I'm not mashing it. I have a 700hp S6 for spirited driving. On the same exact trip, my 2015 1500 Silverado on 34s with a level, crew cab long bed I get 19.6 hand calc).

 

[Duece McCracken]

The 3.6 does not get great gas mileage if you drive with any kind of urgency, well, i have yet to get any real good gas mileage, lmfao! Just be happy you dont have the extra weight of a gladiator. I have a heavy foot, but its a serious struggle to average over 16 mpg for me unless im on a turnpike or something and just sunday driving it.

 

[MEski4x4]

You should use a programmer to adjust and then report back.

Does it really matter? This is the first JL I've had that I actually modded, but on other cars it hasn't made a difference as long as I know my actual speed (which I do).

 

[jludave]

Does it really matter?

Yes. If you have an automatic transmission, the shift points will be off with the incorrect tire size. This can have an affect on gas mileage.

 

[MEski4x4]

Yes. If you have an automatic transmission, the shift points will be off with the incorrect tire size. This can have an affect on gas mileage.

Well the Tazer mini was next on my list, so I'll try that. It *seems* to shift fine. No gear hunting, no high RPMs, plenty of time in 8th.

 

[JSFoster75]

Use the Fuelly App to track your mileage after you adjust the computer for the larger tires.

 

[jeepoch]

@MEski4x4,

Ken, in no way am I experiencing your crappy mileage. My 2019 JL 3.6L 8-speed is lifted on 35's and I routinely get around 8mpg better results. I'm typically between 20 (worst) to 24 (best) driving around metro Denver. That's even with much less ambient air. We're a mile higher up in altitude here.

Even 4 wheeling in the mountains in CO I get better mileage in 4Lo than you are in 2Hi within MA.

Something is certainly wrong. Here are a few things however to compare and contrast.

- 2 door vs 4 door
- Sport vs Rubicon
- I use a Tazer to set my Tire Diameter. But then disconnect it. I use none of it's 'Live' features.
- I do leave my ESS enabled.
- I run nothing less than 91 octane. To prevent or greatly minimize knock potential at altitude.
- My on-road tire pressure is typically around 40 to 41 psi (temperature dependent). I do lower down to low 30's in deep snow and 15psi off-road everywhere.
- I'm pretty much a feather foot. In fact I mostly drive with the fuel economy displayed on the EVIC. I'm certain I am the oddball here.

The last point is likely the most important for my mileage. I have no idea about your driving style but I certainly purchased a Jeep and not a Ferrari. I typically go from 0 to sixty in around a half a minute. I do drive up to 80 frequently on I-25 (to just keep up with traffic) but most of my commutes are rural roads between 30 to 45 mph. Not a lot of stopping and starting. But of course, driving anywhere near metro Denver there are stop lights galore. Yet, I do enjoy the ESS silence however when stopped.

I have no easy silver-bullet answer for you. I'd be way pissed too if I was getting that kind of mileage. That's big truck kinda crap.

Are you experiencing misfires or any other DTC fault codes? Have you every had your engine professionally tuned or had an emissions inspection?

Something as simple as a bad or fouled O2 sensor would be pretty damn detrimental to mileage.

Also running larger than stock tires without calibration adjustment means that you are actualling travelling further in one wheel revolution to what the computer is expecting. So fuel injector pulsewidth management will typically supply more fuel per distance traveled since the engine is actually working a little harder to what it's sensing. You're true speed is actually higher than your indicated speed.

Using cruise control regularly at high speed with an improper tire diameter calibration will only exacerbate this problem since the speedometer error percentage increases (larger delta) with velocity.

So tackle some of the easier stuff first and work your way up. There has to be specific, objective reasons why your mileage is so low.

Are you a good candidate for driving a 4xe hybrid? Trade this thing in if you're unable to sleep at night.

Jay

 

[MEski4x4]

Jay, Thanks for the detailed response. It's definitely not keeping me up at night, as I've been driving it this way for over a year. What made me start thinking about it was my desire for 37s and a lift. My mind started thinking about single digits, and If I wanted that, I would daily my S6 that I can burn through a tank of 93 on in a very short time with the happy pedal.

Engine completely stock, never tuned. Only run high quality gas. Oil changes every 3500mi (i've done less than that in a year at the moment) but I am due for one. No fault codes. No emissions issues. Still under warranty.

My around town driving is definitely killing me. When I say "around town" I mean a 1600s town with 25mph speed limits, constant stop signs, and idiot drivers. My commute is 0.8mi each way at 20mph with a bunch of stops in between. I don't even count that towards mileage because it's just laughable. At 55 on speedo (57) I can squeak out 20mpg (computer) if I'm on flat roads and cruise control.

I know the stubby is killing me when it's windy.

 

[Old Jeeper]

Hey guys - it's been a while but I am finally back in a JLUR and I'm having some issues with absolute trash fuel economy. My daily driving is 30mph or less for maybe a combined 3 miles so I'm not expecting anything great. Currently sitting around 13mpg (was around 10 with leaving it running during the winter). Did a roadtrip to my house up in Maine a few weeks ago, and the Lie-o-meter was 14.6 on the way (but there was a 30mph cross/headwind) and on the way home I squeaked out 15.6mpg. On the trip up, I went through 3/4 of a full tank of 87. Cruise control was set at 70 (which is actually 73) the whole time on the interstate, and up north was 10min trips at 35-55. Transmission had no problems hitting 8th and really never had to drop below 7th except for the occasional monster hill. The only thing to mention (mods below) is I have not adjusted my speedo for the tire height (but I've done the math).

2020 JLUR Hard Top
44k miles
3.6 Pentastar w/8spd
35" Duratracs @ 37PSI
PSC Bruiser Stubby with Warn Zeon 8-S
Factory rear steel bumper
No lift. No engine mods.

I don't see any numbers out of wack. Here is a shot of my 2023 JLR, 35 GY Duratrac @32 psi and 4:88 gears.

Round trip, 175 mi, I 75, on cruise 70% of the time at 71 mph.

 

[John VonJeep]

@MEski4x4,
I'm typically between 20 (worst) to 24 (best) driving around metro Denver.

I believe that Jay is getting this mileage, but I also know that Jay’s mileage is an aberration for a 3.6 Pentastar (unless you drive a constant 45 mpg everywhere). Good for Jay.

For the rest of us, 15 in town and 17-18 on the highway is very typical for a 3.6 on 35s with the 8-speed. OP, your mileage seems low, but you’re also taking very imprecise readings and haven’t adjusted your speedo, so it may actually be perfectly normal.

 

[jlandry287]

Keep in mind if your speedometer is wrong, so is your mileage.

The computer calculates miles by the number of wheel rotations, which changes as tire diameter changes.

Since you haven't adjusted, you're actually getting higher MPG but the computer isn't properly calculating due to the incorrect tire size.

 

[TheRaven]

That's dashboard MPG - but I know it isn't much better than that. The trip north was 172mi and with 2 stops and no mashing of the go-pedal, I burned fairly close to 3/4 of a tank. The way home was just about 1/2 a tank. I've always driven fairly conservatively (coast to stops, don't tailgate/constantly brake) and even getting on the highway I'm not mashing it. I have a 700hp S6 for spirited driving. On the same exact trip, my 2015 1500 Silverado on 34s with a level, crew cab long bed I get 19.6 hand calc).

How did you calculate your mileage? Remember, you can't rely on the vehicle for ANYTHING in those calculations - your speedo is off BECAUSE the computer is not correctly reading mileage. That means that you can't use the mileage readout either, and of course your fuel mileage is off. You would need a outside measurement of mileage, and GPS is generally not reliable enough.

You have two major issues causing the fuel efficiency - your vehicle not being calibrated for the tires, and REALLY HEAVY tires. 35" Duratracs are like 65-68lbs each. On those tires, with your computer properly calibrated, I wouldn't expect more than 17-18mpg in the type of driving you're doing.

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