2019 JLUR 3.6 8speed, 4.88 gearing with 37/12.50/17 Getting 11.5 MPG

[beaups]

speedo is/has been spot on as mentioned in the original post. I have a couple of GPS speedo apps for that very reason. It’s the reason I’ve still been looking for some kind of issue causing the lower than average mph compared to very similar builds.

Ah I missed that. In that case it isn't going to be a gear/tire calibration issue then.

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[jlroman2]

Does exhaust play a big role? I feel like ever since I deleted the muffler and added a high tuck axle back, MPG went down. I recently went with 5:13s from Rubicon 4:10s and running the KM3 39" tires. MPG tends to be about the same. The only difference I see is that now I get 8 speed on the highway all the time.

 

[roaniecowpony]

When I bought my JLUR, I looked at the mileage on the sticker and online forums. I have no desire to check my mileage. I can't think of a good reason to check it.

 

[Lohkay]

I think it's just a matter of drag. I'm running the 3.6L, 4.88 gears, 35" MT on beadlocks and get 15 MPG BUT that's after installing a stubby bumper like yours. When I had the factory bumper, I was getting 18 MPG.

 

[aldo98229]

I wish I didn’t have to check my fuel gauge, either. But recently I almost got stranded out of gas; that’s how fast this sucker goes through it!

 

[OCYJ]

We have a very similar set up it sounds like. I’m running the metal Cloak 3.5 game changer lift. I do have the full under cloak. I’m running Metalcloak fenders. LOD sliders. Ace front and rear bumpers and warn winch. I weigh in it about 5600 pounds.

It's your weight. Well, your Jeep's weight. ?
I have a similar setup to yours and experience similar results. I think the weight of the add-ons, in addition to the effects of tires, lift etc., play a significant role. In your case if you are at 5600 pounds, you have added around 1,100 pounds!
We can't really compare our setups to those with relatively stock setups weighing in at 4500 pounds and averaging 18-20 MPGs.

 

[FrankieGee]

Buy a new OEM air filter
Yours is 3 years old and has been in multiple dusty/pollen conditions
A new air filter is a cheap fix and can only help your current situation.

Have you gotten a 4 wheel allignment? 4 tires travelling together get better wear & mpg than 4 tires fighting each other.....

 

[me109stock]

I have it set at 36.88 I am running Mickey Thompson MTZ's

I'm running 37/12.5R17 MT Trail Boss MTs on B.A.D. Beadlock Wheels - they are heavy! Using the WAZ app to monitor my GPS speed I adjusted my tire size until the MPH on the speedo matched the GPS speed on WAZ. I ended up at a size about three or more steps above 37 (I know they were incremental decimal steps and don't recall the exact number, but I'm thinking 37.28) before everything matched. I'm getting around 17mpg using 5th gear on the highway on the standard 4.10 gears. If your displayed speedo speed is less than the actual GPS speed then you are going to go less calculated miles per gallon than actual, and your MPG will read low (ie if you never changed your tire diameter you would be showing a really slow speed on the speedo and getting really bad MPG). Other factors aside from the weight of the tires and the vehicle are any added mods that affect your wind resistance (rooftop tents, lights, etc.) and of course tire pressure (lower pressure = higher rolling resistance). Terrain will also affect overall MPG. Most of these things are common sense - so just pointing them out in case you overlooked the obvious. It could also be your transmission is slipping? I have no suggestions for how to diagnose that.

 

[lepcat]

It's your weight. Well, your Jeep's weight. ?
I have a similar setup to yours and experience similar results. I think the weight of the add-ons, in addition to the effects of tires, lift etc., play a significant role. In your case if you are at 5600 pounds, you have added around 1,100 pounds!
We can't really compare our setups to those with relatively stock setups weighing in at 4500 pounds and averaging 18-20 MPGs.

I agree that I have a heavy rig. But I am comparing to very very similar rigs. Who consistently get better miles per gallon. I did make a change to the tire size setting the closest I could get to 37. I felt a slight change in shift points. Speedometer is 1 mile an hour off at 65 and 70. In the first tank that was half highway miles at 65 miles an hour. The rest in town. Average 14.8 miles per gallon. Working on the Intown tank now in route will report back. And that is with pen to paper calculation.

 

[lepcat]

Buy a new OEM air filter
Yours is 3 years old and has been in multiple dusty/pollen conditions
A new air filter is a cheap fix and can only help your current situation.

Have you gotten a 4 wheel allignment? 4 tires travelling together get better wear & mpg than 4 tires fighting each other.....

I have cleanable air filters and wash them after every jeeping trip. And yes I’m constantly getting alignments.

 

[lepcat]

I'm running 37/12.5R17 MT Trail Boss MTs on B.A.D. Beadlock Wheels - they are heavy! Using the WAZ app to monitor my GPS speed I adjusted my tire size until the MPH on the speedo matched the GPS speed on WAZ. I ended up at a size about three or more steps above 37 (I know they were incremental decimal steps and don't recall the exact number, but I'm thinking 37.28) before everything matched. I'm getting around 17mpg using 5th gear on the highway on the standard 4.10 gears. If your displayed speedo speed is less than the actual GPS speed then you are going to go less calculated miles per gallon than actual, and your MPG will read low (ie if you never changed your tire diameter you would be showing a really slow speed on the speedo and getting really bad MPG). Other factors aside from the weight of the tires and the vehicle are any added mods that affect your wind resistance (rooftop tents, lights, etc.) and of course tire pressure (lower pressure = higher rolling resistance). Terrain will also affect overall MPG. Most of these things are common sense - so just pointing them out in case you overlooked the obvious. It could also be your transmission is slipping? I have no suggestions for how to diagnose that.

I appreciate your comment. And yes all the items listed I have looked at. See below for a comment. I did up my tire size from the actual tire size. And it did slightly change the shift points. And I am seeing a little better miles per gallon.

 

[BroncoHound]

Buy a new OEM air filter
Yours is 3 years old and has been in multiple dusty/pollen conditions
A new air filter is a cheap fix and can only help your current situation.

Have you gotten a 4 wheel allignment? 4 tires travelling together get better wear & mpg than 4 tires fighting each other.....

A 4-wheel alignment on a Jeep Wrangler isn't worthwhile. The solid rear axle is fixed; it has no ability to adjust camber, caster, or toe (unless you have aftermarket control arms, at which point you have some pinion/caster control). The solid front axle has no camber adjustments and caster and toe can easily be adjusted on a flat driveway with a tape measure.

 

[AndyMcConnell]

From reading all of your responses, I would say you have something wrong with your Jeep. Drag in the drive train or braking systems, or serious engine efficiency issues. We have 37s and 4.88s with the 3.6, 2 inch lift, an offroad front bumper and fenders, and all of the other worst things for efficiency basically, and we are getting a pretty consistent 16 MPG overall. This is our only vehicle, driven for everything, offroad and daily driving. I drive pretty aggressively with it, so not careful for efficiency.

There just shouldn't be any reason you would be getting greater than 25% lower MPGs than ours without something wrong, based on your comments. I would question the re-gear work an also ensure you don't have brake drag, serious toe in or out on the front wheels (thought to lower efficiency that much, you should see that on the tires.) If all of that is ok, engine problems maybe? Pretty crazy that others are seeing anything close to that low on stock or mildly modified Jeeps, as we had 19+ MPG when on 35s and stock 4.10 gears with lift and all.

 

[aldo98229]

37s, lift, 4.88s and 19+ MPG...?

 

[Steph1]

Well, this doesn't seem to have been brought up yet, but... could your e-brake be partially on or something ???? Might sound crazy, but if you are driving and put it in neutral, does it coast a bit or slows down faster than it should ?

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