What MPG are you getting?

Hmmm great info here! Actually that tank at 18.85mpg was heading up to Sedona to meet up w Jamison to pick up a radiator. I was surprised how good the mileage was considering its mostly uphill the whole way. Had to throw her in 4th & step on it pulling the mountains to keep up speed. Expected poor mileage getting up to 3000 rpm but it was actually pretty darn good. Maybe I'll stay out of 5th a little more around town (pretty much all flat) & see how she does.
 
2006, 4.0, 42RLE, 5" lift, 5.13's, 35's.


Terrible, I get terrible mpg.

12 or worse in town. And if not into the wind and lightly weighted I have achieved 16+ on the highway at 65-70.
 
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2002, 4.0, 5 speed, 3.73, 31" tires. I regularly get 14 in the city. 12 on the highway. Doesn't matter, 65, 70, 75 mph, 4th OR 5th, (in 5th, things get HOT). The transmission, not the engine. As in heat through the floor.
I don't hit the highway much, and when I do I stay in 4th.
 
2002, 4.0, 5 speed, 3.73, 31" tires. I regularly get 14 in the city. 12 on the highway. Doesn't matter, 65, 70, 75 mph, 4th OR 5th, (in 5th, things get HOT). The transmission, not the engine. As in heat through the floor.
I don't hit the highway much, and when I do I stay in 4th.

You average less on the highway?
 
The following are things that will effect gas mileage; driving as speeds above 60 mph, engine is operating below the recommended factory temperature, lower tire pressure, brake shoes dragging slightly, old O2 sensors are to name just a few of the more common ones.

My '01 4.0L 5 speed w/ 2" lift, 32's and 4.11s gets 18 mpg highway which is down from 20 mpg since I went to 4.11s (yes I calibrated the speedo), but I drive 70-75 mph on the highway instead of 60 which would be better when trying to squeeze out more MPG.

Man. I could handle 18mpg! 11 highway makes me want to sell it.
 
Yes your 2003 has the 42RLE automatic, that particular transmission drops the rpms so low on the highway that it can cause the engine to lug and get bad mpg.

Do you know what axle ratio is installed? 3.07 or 3.73? If you don't know you can look at the steel tag with your ratio embossed into it at the 9 o'clock position on your differential cover. This one is indicating 3.73 gears are inside the axle. A 3.07 ratio would cause excessively low rpms on the highway which can wreck the mpg, 3.73 isn't far behind with that problem though... all due to how low the 42RLE's .69 Overdrive ratio drops the rpms on the highway.

View attachment 362159

And are you detecting the aroma of gasoline when you're in or around your TJ when it's running? That can indicate the engine is running too rich which will definitely reduce the mpg.

So, from what I’m seeing, it’s 3.73.
Yes your 2003 has the 42RLE automatic, that particular transmission drops the rpms so low on the highway that it can cause the engine to lug and get bad mpg.

Do you know what axle ratio is installed? 3.07 or 3.73? If you don't know you can look at the steel tag with your ratio embossed into it at the 9 o'clock position on your differential cover. This one is indicating 3.73 gears are inside the axle. A 3.07 ratio would cause excessively low rpms on the highway which can wreck the mpg, 3.73 isn't far behind with that problem though... all due to how low the 42RLE's .69 Overdrive ratio drops the rpms on the highway.

View attachment 362159

And are you detecting the aroma of gasoline when you're in or around your TJ when it's running? That can indicate the engine is running too rich which will definitely reduce the mpg.

so, first things first. I went off what the previous owner told me, that the tires are 31”s. They are not. They are 285 75 16 - 33”s.

AND, it’s the 3.73 gearing, according to the cover. I know the PO said he did not get it re geared.

I bet that’s why…also, my speedometer is way slow compared to what I’m actually doing.
 
So, from what I’m seeing, it’s 3.73.


so, first things first. I went off what the original told me, that they’re 31”s. They are not. They are 285 75 16 - 33”s.

AND, it’s the 3.73 gearing, according to the cover. I know the PO said he did not get it re geared.

I bet that’s why.
33's with the 42RLE transmission and 3.73 axle gearing is an absolutely abysmal/terrible combination. For the engine to run well and be in its power band to not lug (which gives poor mpg) and generate the power the engine was designed to produce it'd require no less than 4.88 but 5.13 in the axles would be an even better choice. Driving two TJs configured alike with 33's and 42RLE but one with 3.73 and one with 4.88 or 5.13 you'd then be convinced to beg, borrow, or steal the $$$ to install the one of those two preferable ratios lol.

Regearing my TJ I bought used came with the 42RLE, 4.88 gears, and 35" tires. It lugged and could barely get out of its own way on the highway. Not to mention its best mpg was 11 mpg. I regeared it to 5.38 which finally gave it tolerable highway rpms (2450 or so at 70) and bumped the mpg up to 14.6. It became an altogether much more pleasurable Jeep to drive.
 
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Hey all.

Just read a thread about folks getting 17mpg and 18mpg in their TJs.

I have a 4.0, auto, running a 3.5” lift and 31s. Tires are bf goodrich mudterrains.

My average mpg is 10mpg, with 11.5mpg being my highest. That was me doing everything I could to keep in the overdrive “gear” with RPMs below 3k.

When I read the higher mpgs, got me thinking - is something wrong / old with mine? I do know I need a track bar replacement as well as the steering stabilizer replaced. Maybe that’s creating extra work?

Thanks all,

J

Just re-read your initial post - If you are turning near 3000rpm in OD currently it seems you would running near 80mph...wtf?

Your speedo should only be about 5mph off like mine once was.
 
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2002, 4.0, 5 speed, 3.73, 31" tires. I regularly get 14 in the city. 12 on the highway. Doesn't matter, 65, 70, 75 mph, 4th OR 5th, (in 5th, things get HOT). The transmission, not the engine. As in heat through the floor.
I don't hit the highway much, and when I do I stay in 4th.

You average less on the highway?

I do. I've replaced every sensor or component that my research, (google, as well as here) said might affect fuel mileage to no effect. I've had nobody offer any theory as to why. Literally, the closest thing to helpful anybody has said is, "Well, Jeeps don't get good mileage", and then posting that pic of a cow being more aerodynamic that a Jeep. That, and, "Just stop keeping track".
 
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I do. I've replaced every sensor or component that my research, (google, as well as here) said might affect fuel mileage to no effect. I've had nobody offer any theory as to why. Literally, the closest thing to helpful anybody has said is, "Well, Jeeps don't get good mileage", and then posting that pic of a cow being more aerodynamic that a Jeep. That, and, "Just stop keeping track".

That would drive me crazy... o_O
 
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Driving style makes a larger difference than being geared properly IMO. The only 2 Jeeps I've ever owned (20) that got 17-17.5 mpg highway on a regular basis for years were my 98' 5 speed on 35s with stock 3.73 gears and my 05' 6 speed with stock 3.73 gears and 35s. Both had the speedo gears changed. Highway top speed was 60 mph. Anything above 70 dropped it to SHIT levels. MYTH BUSTERS should do an episode on this topic. :unsure: