I'd like to share my experiences with mpg on two Wranglers. Please bear with me cause I'm trying to give all the data I can:

Our current Wrangler: 2012 2dr Rubicon hardtop with the 6 speed manual and 4.10 gears, 2300 miles on it at this point.
Previous Wrangler: 2010 2dr Sport hardtop with the 6 speed manual and 3.73 gears. It had 23K miles when we traded it.

With the change in the manual's 6th gear ratio and the 4.10 vs the 3.73, our new one spins only 4.3% faster (about 85rpm higher at 60mph). Yet the mileage we're getting is more like 12% lower (18.5 vs 21). These are both calculated mpgs.

We're driving the same routes and are trying to drive in a similar fuel-conserving manner while still flowing with traffic. On the 2010 I was using the Superchip's 89 octane tune and ran 91 octane fuel. This fuel was said not to contain ethanol. On the new one we're running 87 octane that has 10% ethanol. I believe the 10% ethanol accounts for about a 3% loss of heat energy, right? So maybe that accounts for some of the mileage loss. I also ran the Mopar CAI on the 2010. I ran a tank of the 91 octane "w/o ethanol", not for the octane but to see if the "no ethanol" would yield more mpg. It appeared that the mpg came up from the 18.5 to about 19. That's an increase close the the 3% diff in heat energy so I convinced myself that made sense.

Do you think the Rubicon's tires have that much more rolling resistance compared to the Sport's? They are both roughly 32" dia, etc. The ride height of the Rubicon is no more than an inch higher than the 2010. I'll be running a set of Blizzaks this winter so will watch for any change in mpg when I switch over to them.

I also understand the fuel formulation is different from summer to winter and the 21mpg I'm quoting on the 2010 was through the summer months. The 18.5mpg we're getting on the 2012 has been over the last 6 weeks or so that have (I'd imagine) been on the winter fuel.

The Pentastar really makes the Jeep nice to drive. The engine's extra torque around 1800-2K rpm makes the need to downshift for small hills or headwinds much less frequent compared to the 3.8. It's very smooth and responsive. There are times I enjoy the upper end power but for the most part I've been driving conservatively like I generally did in the 2010. I towed a narrow enclosed trailer last week with one snowmobile inside (a Ski-Doo of course....) and the mpg didn't seem to drop very much from the 18.5. I guess it fit pretty well behind the slipstream of the Wrangler.

I'm very happy with the performance of the Pentastar thus far but am surprised this modern engine having less displacement (about 5.2% less) isn't yielding at least as good mpg as the 3.8 did, and I"m looking for anyone's insight on what might explain the difference.

Thanks!

 

Stock vs. stock, I'd put my '11 up against any '12 out there in a MPG war. This thing was putting up 19.2 MPG consistently while on stock tires on my daily commute, which surpasses every 4x4 I have ever owned except my Liberty CRD.

 

My stock 2012 Jk Sport gets a 19-21 average constantly. Never even seen it below 19. Roughly 4k miles on it.

 

I've read that the vvt doesn't kick in until 5,000 miles.

 

I have read the same thing. Stated that the ECM monitors driving habits for the first 5K before actually mapping it and letting loose. It actually showed how it goes in increments on mileage monitoring driving habits.

 

I drove mine for the first time today other than bringing it home from the dealership. I have a 15 mile commute to work and at 65 all the way there with some moderate hills I averaged 17.2. I have an auto Rubi with the 4:10 gear. I was doing a little better with my 3.8 but we shall see as mileage progresses...

 

when mine was stock, 11 manual 2dr sport with 3.21 gears, on trips going 70 to 75mph i was getting about 26mpg and around town i was averaging about 20-21mpg


I miss those numbers sometimes

 

Do you have a source for that? I would like to read it.

I drive like an old man most of the time, hope I'm not going to end up with an old man motor.

 

My 09 3.8 auto 3.73 2 door X mileage is highly variable. I've kept a detailed fuel log from the beginning. According to my data there is no question that this vehicle returns better mileage once broken in - at roughly 3-4 thousand miles.

So far the lifetime average over 30k miles is 17mpg US with plenty of running around a hilly city (Vancouver, BC).

My highway mileage NOW averages 23.2mpg US (27.8mpg Imp). Earlier on - the same trips netted 20-21mpg US. Of course this is using the same fuel, same tire pressures, maintenance etc. - otherwise the stated numbers would be useless.

This is also "driving for mileage" but keeping up with traffic.

Fuel mileage is science: acceleration, wind, tire and various friction resistances vs energy in the fuel. The optimum mileage for my vehicle seems to be between 50 - 55mph. At 65mph (no wind) mileage starts to noticeably decline due to air resistance which is a major factor for any Wrangler.

One of the issues with more powerful engines comes down to driving technique. Quicker acceleration and higher speeds - although easier with the new Pentastar - will bring fuel mileage far below a 3.8 that's driven at a more normal pace.

This is the case for any vehicle I've owned. At present I also run a 2008 F150 Lariat with the "old" 5.4L and 4 speed automatic. I notice in forums that I am acheiving higher highway fuel mileage than the newer trucks - including the 3.5 ecoboost. Quite simply there is no engine built in the last 10+ years that "wastes" fuel. We're pushing around the same mass with the same friction resistances. How and where you drive is far, far more important than the subtle efficiency differences that may be claimed by our beloved truck manufacturers from year to year.

 

Gas type may play a factor also, I'm between 17.6 & 18.6 variable driving characteristics, BUT we're on winter mix in gas here in the Northeast not sure if the whole country does it but there's more crap in the gas for winter months here so my mileage would not be great till spring/summer

I still get better mileage than my KJ & TJ did though