Just out of curiosity, what kind of gas mileage are you getting with a JKU or JLU (please indicate which one you have) with 37's? What gears and axles do you have? If you have different size tires please feel free to post as well as long as you provide your specs.
JKU, 4.56 gears with an Auto Trans, 37 inch tires. I stopped looking because it's not great 😀
Let me pay attention and get you some numbers, however I can say that last year coming back from Sierra Trek I was doing 45-50 MPH most of the way home and I was shocked how much better the mileage was, I normally stick in the 65-70 range on the freeway (I was trying to stay in radio contact with a certain 4Runner I drove out with) 😇
JLU, 37s, 4.88 Gears
I get around 14-15, but can get up to 19 on the hwy, or 25 if I’m following David in his Samurai.
21 JLU Willys 3.6L v6, stock gears 3.54 with the 8 speed auto trans. Stock axles Dana 30 in front and Dana44 in rear. Rear axle has limited slip. Open diff in front. I am running 37 in KO2 BFG's which run small at about 36 inches. My average mpg is 13.9. I never see 8th gear unless I am going down hill on the freeway with a good tail wind. I know I should re-gear to get the power back but for the medium wheeling I do it seems to work OK for me.
My JLU is showing just under 14 mpg. I think the speedo may be off a little too. The previous owner went form 35's to 37's right before trading it in, so perhaps it needs to be recalibrated.
Jeff_R said My JLU is showing just under 14 mpg. I think the speedo may be off a little too. The previous owner went form 35's to 37's right before trading it in, so perhaps it needs to be recalibrated.
Probably. If you don't have a way to adjust the tire size then yea i would have it checked. I use Jscan to adjust all of my settings in my jeep. A Jscan license for a single VIN is about $20 and the Vgate vLinker MC+ Bluetooth OBD2 Car Diagnostic Scan Tool costs about $60. The security cable costs about $15. So in total I spent $95 vs buying the mini tazer at $330.
Dropping your freeway speed down to 65 does wonders for mileage on account of the aerodynamics (or lack thereof). Expect 14-15 driving 75 and north of 20 if you can stay 55. These things are way faster than the TJ you are used to so if you can drive at the same speed you accelerated everywhere in the TJ you will hit high teens. Keep your foot out of it or get a diesel if you want better mileage.
Tire size and weight are also huge impacts. From a stock rig (JL) without modifying driving style and doing 75+ on the freeway, jumping from the 255 street tires to the 285 rubicon ATs was a 1-2mpg hit and the rubicon or willys MTs were another 1 MPG. Expect ~1mpg loss per size jump (stock to rubicon 33s, 35s, then 37s) and 1-2 mpgs going from ATs to heavier MTs.
For a JK with the 3.6 and 5speed auto figure 1mpg less from all the above and 2-3mpg less with the older 3.8.
My main concern is beginning to understand the potential range of my JLU. Looks like it is about 240 miles before I need to really worry. I'm trying to plan future mods. I currently don't have the ability to carry external fuel tanks so I'm trying to figure the out JLU set up going forward.
Quick and dirty check on speedometer calibration is to compare GPS speed on phone to actual speedometer.
Wait, I lied, I have 4:88 gears. I just checked the current stats in the computer and it is saying 16.3 MPG.
Driving profile for months has just been 1/3 getting to and from the freeway and 2/3 on the freeway between El Dorado and Rancho Cordova, not trail loaded.
JKU, manual, UD60s, 5.38, 38s, 34psi, 14-ish mpg
Jeff_R said My main concern is beginning to understand the potential range of my JLU. Looks like it is about 240 miles before I need to really worry. I'm trying to plan future mods. I currently don't have the ability to carry external fuel tanks so I'm trying to figure the out JLU set up going forward.
You wont need any extra fuel for anything we do. My LJ drops to 6mpg in 4 low but these hang out in the 10-12 range. Expect to roll out of the rubicon with over half a tank. Maybe bring 5 gallons for Sierra Trek but even then your probably wont use it.
kris_olof said
You wont need any extra fuel for anything we do. My LJ drops to 6mpg in 4 low but these hang out in the 10-12 range. Expect to roll out of the rubicon with over half a tank. Maybe bring 5 gallons for Sierra Trek but even then your probably wont use it.
I'm thinking more about range on trips like the ones Jeff Light is doing. One reason I bought the JLU is to be able to travel in greater comfort and have more space for Kathy to join me on some of the overlanding or touring type of runs. Based on my current setup, I don't see any way to carry additional fuel externally and I don't like the idea of carrying fuel inside my vehicles.
My brother had one of these on his JKU and it worked great. He would use it to refuel between Carson City and Las Vegas.
https://www.northridge4x4.com/part/fuel-tanks/10305031ab-aev-10-gallon-gas-caddy-black
Pricey but with all the money you saved..............
Sloguy said My brother had one of these on his JKU and it worked great. He would use it to refuel between Carson City and Las Vegas. https://www.northridge4x4.com/part/fuel-tanks/10305031ab-aev-10-gallon-gas-caddy-black Pricey but with all the money you saved..............
I wonder if it would work with a 37" spare tire?
With all my road trips, I have never had to use extra gas from cans I carry on my Red Jeep, plenty of gas stations along the way, except for a longer off road trip I did in Death Valley. There are plenty of gas can spare tire mounts like Rotopax that make it easy to carry 4 - 6 extra gallons depending on can size.....put probably reduces your MPG due to weight and areodynamics though, lol. There are window mounts also that would allow you to carry even more Rotopax cans. My Red Jeep has 37s, no problem with a spare tire mount and two cans.
I also have a spare tire mount for gas cans for my Green Jeep with 38s but have not had to use it yet.
When I go to Sierra Trek I take ten extra gallons of fuel with me. I have five on my TJ and I bring another five in my truck. I like the idea of having extra fuel whether it might be for me or for someone else who might need it. I have a license plate relocation kit so my license plate, plate light and third brake light are mounted in the center of my spare tire. My spare tire sticks out a lot so I don't want anything that will make it stick out even more. I bought a receiver mount skid plate/step to protect the spare tried so that when I come off a large rock or a rock shelf I hopefully won't hit the tire and damage the tailgate.
Jeff_R saidSloguy said My brother had one of these on his JKU and it worked great. He would use it to refuel between Carson City and Las Vegas. https://www.northridge4x4.com/part/fuel-tanks/10305031ab-aev-10-gallon-gas-caddy-black Pricey but with all the money you saved..............I wonder if it would work with a 37" spare tire?
Looks like you have to have the AEV tire carrier for this to work. Otherwise it does support 37" tires
For a "special occasions only" situation:
https://rockslideengineering.com/product/ez-rack-kit/
or
https://www.jcroffroad.com/product/UNI-STB.html
For a more permanent mount:
https://garvinracks.com/products/jeep-jl-rotopax-mount-factory-tailgate-20400-20401
or add an aftermarket bumper/tire carrier with a can mount.
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