Around town, the 4 cyl should get slightly better mileage... all else being equal. On the highway, the 4.0L will usually do a little better.
But, they are close enough that the driver is the biggest difference. I had a buddy with a 2.5L when I was running my 4.0 YJ. I almost always got better mileage... and I had 35s with 4.10 gears. He was running 31s and 4.10s.
the weight of the drivers foot makes a difference. currently im averaging 16-19 with my 4.0 on 33's on 3.07's. my uncle has a 2.5 and hes doing about the same if not a little better son stock tires and 4.10's
x3 on the gas pedal. I skinny pedal everything I drive (well, MOST of the time) and I get away with better mileage than what the manufacturer states. Our highlander is only supposed to do 19mpg average on the highway, 15 city, and i'm getting 20 city and 24 highway.
I can't really tell you about the 2.5L fuel efficiency though. Mine has been having issues causing it to SUCK the gas away...
if looking at the big picture you might squeeze 1 mpg more out of a 4cyl, but at that rate just get a 4.0 and get more power. the main problem with the 4cyl is that its not powerful enough for a 4500lb vehicle. the 6cyl is not really powerful enough either but its better.
Around town the 4 cylinder is fine, but ours just took a 400 mile trip through the hills/mountains of Western CT, NY, and PA. Constant downshifting and pedal down. Averaged 14.5 MPG. Once the grade levelled out milage went up around 16-17. Around town with 31's with 410 gears we're getting around 15-17 depending on which daughter is driving. Given the option, I'd opt for the 6 cyl if you have a light foot or plan any highway driving with grades. Off road and around town the 2.5 has plenty of power and probably the same mileage.
Great advice. I just got my new jeep with the 3.8 v6. I lifted it 3" and put 295/75R16 Dick Cepek rims and Nitto Grapplers and my mileage went to hell in a hand basket. Not sure so this seems like the place to ask. Would I be better dropping the tire size? Width or height, or would I be better off changing the gears?? This is my daily driver and I would be excited to get better than 12 city 15 hwy. Thanks for any advice.
^Your initial post clearly states that neither the 4 or 6 cylinder engines have an appropriate power level for the Jeeps.
You forget that a Jeep is not made to go fast. Anything over 80 and you're just stupid for going that fast. It's a brick, and moves through the air as such. The 4 cylinder is plenty for a Jeep. A 6 cylinder has the added torque and power, but honestly, unless your rig is 100% for offroad rescue then that is all you will need.
i'm not talking about going fast, or power. i'm talking from a mpg standpoint which the thread is about.
if jeeps had more horsepower then they would get better mpg, people who swap in V8's get better mpg b/c they have more hp.
example 3.8 had 203 hp and got basically the same mpg as a the 193 hp 4.0 16/19, 3.6 has 285hp and mpg went up to to 17/21, yes its slightly smaller but the difference between the 2.5 and the 4.0 EPA wise was 16/19, and 17/20. and that's a big difference for an even smaller gain.
i don't want to get into an argument, it was just my opinion.
i apologize if i insulted your jeep.
Generally speaking, gas mileage is not entirely a factor of your engine size, torque output, or horsepower rating. The determining factor is the amount of lead in your foot.
If you're constantly pushing it to the floor, or using it heavily, then you're going to get horrible gas mileage, and it doesn't matter if you drive a Prius or a Jeep. A heavier foot means lower gas mileage.
That being said, a V8 does have the potential to have better gas mileage than a 4 cylinder, but again your foot decides that. Who wants to build a powerplant only to light foot it around town?