interesting fuel mileage
Thread Starter
JK Freak
Joined: Oct 2015
Posts: 542
Likes: 10
From: Austin, TX
interesting fuel mileage
I have a manual 2015 JKU with 3.73 gears (1.5-2.5" lift, steel bumpers, no other mods), and I got new tires about 3K ago. The tires (Cooper Discoverer AT3 265/70R18) are nearly 33" actual. The speedo is calibrated by matching GPS speed using a Flashcal. When they put the tires on they set the tire pressure to something like 32-34 psi. I thought I'd give it a shot that way, since that's the most commonly recommended range here on JKF and elsewhere on the internet. I got an average of about 15.4mpg during the first few thousand miles with this tire pressure. I initially blamed the tires for what I thought was pretty bad gas mileage compared with what I got on the Duelers for the first 22K miles since I bought the Jeep.
We took a trip last week to South Padre which included some ~800 highway/freeway driving (avg. 75-80mph) each way, and two "end of the island" trips down the beach totaling about 100 miles of beach/sand/offroad in 4wd at max speed of about 30mph in 3rd gear (MT). Before taking off for the trip I adjusted the tire pressure back to what I was running with the Duelers, 38psi. I averaged about 18.5mpg on this entire ~1000 mile trip including the beach/sand sections and a half a week of commuting to and from work since returning.
That's a +3mpg difference, or about 20% improvement, by just adding 4-6 psi.
Some other things I noticed in the past weeks driving and monitoring the MPG:
My JKU gets better gas mileage when the revs are kept above 2K rpm cruising. Even though the "ECO" light will come on if you shift into 6th at 50mph trying to convince you that it uses less gas, it doesn't. I'm sure this is because the engine is simply not as efficient in that rev range. Keeping between 2K and about 2.5K rpm cruising seems to be the sweet spot.
Also wind plays a huge role on the highway, of course. My trip from Austin to S. Padre was nearly due south and back north. In TX, especially South Texas, we get a near constant south wind this time of year. Once south of Kingsville, it was noticeable as a serious impediment driving down, so much so that the max speed of my Jeep when going up slight hills (and if you know South Texas, you know the hills are all slight) was about 80mph in 6th with WOT. Gas mileage coming home, north, with the wind at my back, was almost 2mpg better than it was heading south into the wind.
While I often complain about the Jeep's poor fuel economy, the reality is that we got consistently about 19-22 in our 2007 Honda Pilot 2WD with VCT and it has far better aerodynamics and much smaller tires, not to mention being ~500 lb lighter. And we got about 20 normally in our manual AWD Honda Element with a 2.4L 4 cylinder engine. If we went on a long road trip and set the cruise under 60mph we could get close to 25mpg in the Element but it was pretty awful at 70+mph, sometimes barely cracking 20. My Miata and my wife's Lexus IS250 both got a pretty consistent 25mpg and required premium fuel, and my wife's '13 Expedition 2WD got almost identical gas mileage to my Jeep on our S. Padre trip (we took 2 cars, 6 people...), measured at the gas pump. The reality is, 18.5mpg in a 2" lifted JKU with 33" tires on regular gas is, IMHO, pretty excellent.
We took a trip last week to South Padre which included some ~800 highway/freeway driving (avg. 75-80mph) each way, and two "end of the island" trips down the beach totaling about 100 miles of beach/sand/offroad in 4wd at max speed of about 30mph in 3rd gear (MT). Before taking off for the trip I adjusted the tire pressure back to what I was running with the Duelers, 38psi. I averaged about 18.5mpg on this entire ~1000 mile trip including the beach/sand sections and a half a week of commuting to and from work since returning.
That's a +3mpg difference, or about 20% improvement, by just adding 4-6 psi.
Some other things I noticed in the past weeks driving and monitoring the MPG:
My JKU gets better gas mileage when the revs are kept above 2K rpm cruising. Even though the "ECO" light will come on if you shift into 6th at 50mph trying to convince you that it uses less gas, it doesn't. I'm sure this is because the engine is simply not as efficient in that rev range. Keeping between 2K and about 2.5K rpm cruising seems to be the sweet spot.
Also wind plays a huge role on the highway, of course. My trip from Austin to S. Padre was nearly due south and back north. In TX, especially South Texas, we get a near constant south wind this time of year. Once south of Kingsville, it was noticeable as a serious impediment driving down, so much so that the max speed of my Jeep when going up slight hills (and if you know South Texas, you know the hills are all slight) was about 80mph in 6th with WOT. Gas mileage coming home, north, with the wind at my back, was almost 2mpg better than it was heading south into the wind.
While I often complain about the Jeep's poor fuel economy, the reality is that we got consistently about 19-22 in our 2007 Honda Pilot 2WD with VCT and it has far better aerodynamics and much smaller tires, not to mention being ~500 lb lighter. And we got about 20 normally in our manual AWD Honda Element with a 2.4L 4 cylinder engine. If we went on a long road trip and set the cruise under 60mph we could get close to 25mpg in the Element but it was pretty awful at 70+mph, sometimes barely cracking 20. My Miata and my wife's Lexus IS250 both got a pretty consistent 25mpg and required premium fuel, and my wife's '13 Expedition 2WD got almost identical gas mileage to my Jeep on our S. Padre trip (we took 2 cars, 6 people...), measured at the gas pump. The reality is, 18.5mpg in a 2" lifted JKU with 33" tires on regular gas is, IMHO, pretty excellent.