Ways to improve mileage in a JKU?

[GFA]

I recently wrapped up a 7650 mile trip from NC to several of the Rocky Mountain states and back and already can't wait to do it again next year. But, the mileage on the highway is horrible to the point I might tow it with my fathers f350 next year.. Here's my current setup

2010 JKU auto.
285 duratrac's
513 gears
Gobi rack (was empty for the trip)
2.5" lift

At the slower speeds, (55-60) I averaged around 16mpg roughly. On the Montana backroads we somehow managed to squeak out 23.89mpg over 120 miles. But the highway is a whole different story, I'm lucky to get 12mpg at 70mph. My trip consisted of nearly 5k miles at those speeds just to get out west and back home so the bulk of my mileage is very costly.

At 70mph, my rpms are just a hair under 2700, would it be stupid to assume 35's would get my rpms down a bit and possibly increase mileage slightly?

I'm debating a ripp sc as it would be nice to get the added power along with the reported 2mpg gain but I feel like I'd be better off trading up to a 2012+ JKUR auto for a few K more. I would do the same 2.5 lift and 285's but I'm assuming the stock 4.10 gears would be fine. When leaving Great Falls for GNP I was in a 30-60mph headwind and could not break 55mph yet was passed by a newer JKUR on 285's like I was tied to a tree and he had 2 14' kayaks strapped to the roof..

Plans are to also get a teardrop trailer in the next year or so also.

Any thoughts?

 

[expedition4x4]

Gears seem deep for the tires, I have stock 3.73 gears with 35x12.50x17 and I averaged 18.5 and stayed in 5th gear as opposed to 6th to keep it at 2100 when on highways driving north through California and Oregon in June. Is your jeep a standard or Auto? the differnt engine configurations can also account for a bit of difference.

 

[Septu]

I recently wrapped up a 7650 mile trip from NC to several of the Rocky Mountain states and back and already can't wait to do it again next year. But, the mileage on the highway is horrible to the point I might tow it with my fathers f350 next year.. Here's my current setup

2010 JKU auto.
285 duratrac's
513 gears
Gobi rack (was empty for the trip)
2.5" lift

At the slower speeds, (55-60) I averaged around 16mpg roughly. On the Montana backroads we somehow managed to squeak out 23.89mpg over 120 miles. But the highway is a whole different story, I'm lucky to get 12mpg at 70mph. My trip consisted of nearly 5k miles at those speeds just to get out west and back home so the bulk of my mileage is very costly.

At 70mph, my rpms are just a hair under 2700, would it be stupid to assume 35's would get my rpms down a bit and possibly increase mileage slightly?

I'm debating a ripp sc as it would be nice to get the added power along with the reported 2mpg gain but I feel like I'd be better off trading up to a 2012+ JKUR auto for a few K more. I would do the same 2.5 lift and 285's but I'm assuming the stock 4.10 gears would be fine. When leaving Great Falls for GNP I was in a 30-60mph headwind and could not break 55mph yet was passed by a newer JKUR on 285's like I was tied to a tree and he had 2 14' kayaks strapped to the roof..

Plans are to also get a teardrop trailer in the next year or so also.

Any thoughts?

The 285s are what... 32s? I found my stock 2012 JKUR (32s, auto, 4.10s) geared too low, and when doing 60 my RPMs were ~2500. Completely stock, my best tank was 19.9 MPG at 60ish (was on a twisty remote highway). With 33s, my RPMs at 60 are around 2250. My best tank pre lift was 21 MPG (with heavy 33s, towing trailer, bumpers n winch). My best tank post lift was 18 MPG. But driving 70 vs driving 60 makes a huge difference on your mileage... especially when your RPMs are at 2700.

Light 35s (and I emphasize on light) might help with the mileage due to getting the RPM's down to something more reasonable... but more likely you'll still have poor mileage... it just won't get worse. As you saw with your backroads travel vs your interstate travel... speed will make a much bigger impact.

 

[Chris85xlt]

i bet tossing the roof rack and using less aggressive tires will help better your gas mileage. Also the really low gearing/tire size might play a role too

i get 16-17mpg on the highway doing 75+ mph

my best at stock was 21mpg doing 60-65mph

 

[Longtallsally]

Roof rack = fail
Big tires = fail
70 mph = fail

So I'll just present some anecdotal info, and it's not completely applicable as I've got the new engine and a 6 speed ('12 JKUR), but maybe it will give you some data points. I'm still on the stock size tires and 4.10s to be clear.

Roof rack:
Just by putting a simple Yakima one with a basket on the hard top costs me 2-3 mpg at freeway speed. Yes, I think the Gobi rocks and is cool, but if economy is on your mind, ditch the thing. I'm so determined on this that I think we get the same or better economy towing our 3k+ lb camper as we would by having the sail of a rack up there- empty or not. Remember, the JK is still a rolling refrigerator so the worse you make that, the bigger hit to the economy.

Big tires:
Although it has been noted and I agree that yours aren't that large, any time you put bigger tires on, regardless of gearing, you are still increasing rolling resistance and weight and thus the amount of power to get and keep them going. In my opinion I think if you have put different fender flares on, that can impact the aero of the vehicle in the same manner as the rack.

Speed:
I have found that the moment you go at or over 70 mph, yer screwed. The truly sweet spot is 55-60 for my setup.

Combine these three in addition to the weight of your gear and passengers and you have a triumvirate of fail.

So for data points, when mine was new and stock, as long as I kept it under 70 I could get over 20 mpg pretty easily and with minimal effort. I now have 2" springs, still the stock tire size, and about 300 lbs of winch and armor as well which generally gets me around 18-19 (19 if I'm at a consistent speed on the freeway at under 70). With the camper and no rack, I've gotten as good as 17 and as low as 12 or so. I'd say as long as I stick to 55mph (here in Kalifornistan when towing) and I don't have a gnarly headwind I get around 15 as an honest number. Unloaded driving around town only I get 15-17, unless the top and doors are off where the loss of 400 lbs helps a good bit.

Is there a simple answer for you? No, I don't think so. You put a blower on there, and I promise it will be worse for a while as you enjoy hitting happy button, so I personally wouldn't kid myself on that one. The only real solution(s) in the immediate for you would be to verify your tire size to gearing, and to get rid of the rack in addition to obvious lower speeds. I hope this was at least a little beneficial.

 

[eternus]

I have nothing to back this up but... If you're driving an automatic then there are many claims that just using a flashpaq to improve your shift points can help with a few MPGs as well. It'd be helpful to hear from someone with a 3.8L that has used it to confirm if that'll help. Otherwise, you might start searching the threads explicitly about the benefits of flashing.

 

[1stDeuce]

You probably got passed by a 6-speed running in 5th... The overdrive ratio in the auto is not so good, and dropping to 4th with 5.13's is going to get you more speed, but at like 4500 RPM's, so using a lot of fuel. The 5.13's probably allow you to stay in OD longer, which is generally better, but you're auto lacks the gear ratio choices that the manual has.

I had a roof rack on my TJ for a while... It easily took my mileage down 3mpg. Add a headwind and I was in 4th at WOT at 55mph getting like 10mph. (Wyoming...)

Ditch the rack. Drive slower. (I run 68mph tops) Learn to stop only for fuel, or hit a rest area instead of an exit if you need a stop but not fuel. That's how you get good mileage w/o your trip taking forever.

 

[precision powder]

For what it is worth I pulled 23.8mpg when I was stock, averaged 23 (3.8, stock tiny 16s). After I put rubicon wheels and tires on I still managed to get an average of 20-21 mpg. I never drive the highway, all city or normal roads.

It really is more about how you drive than anything. Coast into stops, take off easy as lights, I shift around 2100rpm, coast down hills, avoid passing people, drive roughly around half a tank of fuel, etc. I also have a hard top, I took my back seat out, but I have roughly 110 pounds of gear in the back that is in there all the time. Keep your tires inflated to reduce friction.


Best I ever got was in my big turbo diesel vw, I was averaging 71.4 in a car with a 1.6L with a monster turbo and a roof rack. How you drive is more important than anything else.

 

[bluehash]

I have a similar setup to yours. Gobi + 4.10 + Stock tires

I made a 900 mile trip through Maine recently.. 20mpg average. My sweetspot speed is 60mph. Anything over that kills mileage.

 

[jungblud]

Wind drag increases exponentially as the frontal area of a vehicle increases. Lose the rack.

Also go with all terrains next set of tires.

 

[HAFICON]

For what it is not worth:

2012 JKU Auto loaded kind of heavy.
Bumpers winch rack all the fixxings.
4.88 and 315/70/17 Duratracs.

Drove from Cape Cod Ma. To south Alabama then back to Ma. Was a steady 13.5mpg speed was higher than it should have been(above 70). Also in Alabama highway speed limit is 70mph. Made a similuar trip when it was new and fully stock 3.73s 255/75/18 and I averaged 18-20.

 

[GFA]

I agree I'm geared to deep but there's no changing that now. I got my gearing advice from the local gear shop and people more into hardcore wheeling than long distance travel. I will say they were right about the off road performance of 5.13's at least..

I also can't say that I noticed a difference in fuel mileage after adding the gobi though I'm sure there is a change for the worse. I think I'll try taking it off for awhile to see if there's a significant difference without it. I'm not opposed to getting rid of it after only three months of having it. I miss my soft top but couldn't stand to leave it on with all the noise it made because of the gobi. I do have an M416 that will carry all our gear but I was hoping to not have to tow it around on every trip which is why I bought the gobi. I'll have to compare the two to see which is a bigger fuel burn.

If I were to slow down to 60-65 on the highways around here it would be about as dangerous as driving a horse drawn buggy on the interstate. People are awfully impatient...

I have a feeling I'll be getting rid of this thing by next spring as I really want a teardrop trailer but it would be painful towing one with this current setup. I'm just not sure that a newer one would be that much better either..

 

[collkid]

oorrrr...

Do what I did. Buy a $1500 Honda beater and get 40mpg.

Pays for itself in months.

 

[Idahoan]

Or trade it on a 2012 or newer rubicon...

 

[Hilldweller]

Despite all advice, JKs have notoriously different mpgs even with the same set-up.

Make your tires lighter and lose the rack. 255/80-17 or 255/85-16 Cooper ST-Maxx will help. 4.88 gears will help. A Pentastar will help.
But just be ready to face the fact that somebody with the same set-up will get better mpgs.

This was my 2008 JK with 255/85-16 BFGs, 4.56s, and autotranny. About 14mpg on the highway with the trailer. Could barely hit 63 mph.

This is us now with a 2014 JKU, 3.73s, 255/80-17 ST-Maxx, manual trans. 14mpg on the highway with the very heavy teardrop.

The JKU gets 18 solid around town though and about 23 on rural roads without the trailer.
Wranglers are bricks.