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I just bought a clean 98 TJ 4.0L 31" tires auto trans w/83 K miles. I tuned it up w/plugs, cap,rotor, wires. Running middle grade gas. MPG I got so far is low 14.6 high 16.8. I did run with ac some of the time. Sound about right? I don't have a heavy foot, but not babying either.What do others get-I know lots of variables ( manual trans, different axle ratios,tires, 4-6 cyl engines, etc). just wondering. BTW engine idle up a little since tune-up, so it may be a little more efficent-maybe best MPG I am gonna see?.
 

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Yeah, run 87 octane fuel in your jeep. Any more will be harder for the engine to burn and can leave deposits in the engine.

With 3.73 gears, 33" tires, 5 speed, and 4.0, I get 11-12mpg city and 15-16mpg highway.
 

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Consumer Reports did an article a decade or so ago about mid grade gas and how it was a rip off. Snake oil. A in between way to step increase price to premium. So unless your vehicle calls for premium, stick with the cheap stuff. Lower octane burns better and saves you money!
 

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Your MPG is normal.
 

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You sound like you have a great running Jeep. The only gas "upgrade" would be to find a station with no ethanol .
Don't believe the hype on air intakes, exhaust upgrades, resetting your computer or any other claim that you are going to get better than what you are running.

I run pretty consistent 16/18 mpg
 

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Mine is the 6-speed, but you are getting pretty much the same range that I usually get. I do a little better on an all-highway trip.
 

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I've had my stock LJ a month and average 16.77mpg. Rubicon package, 4.0L, 6 speed manual, 4.10 gears, dana 44's front/rear on 31's. Use 10w30 motor oil, haven't looked at the plugs just yet as I'm pretty happy with the gas mileage (threw that in there cause I've read some entertaining threads on oil/plug/gas mileage).
Was averaging 17.56mpg while the hard top was on. Now flip-flopping between topless and soft top (damn New England rainy season) it been around 16.11mpg.
I use a free Android app called aCar. Pretty useful, lots of extras, like how much it costs you daily to run your car(s) figuring in your insurance, gas, oil changes, etc, etc, etc. Reminders when maintenance is due.
 

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I just bought a clean 98 TJ 4.0L 31" tires auto trans w/83 K miles. I tuned it up w/plugs, cap,rotor, wires. Running middle grade gas. MPG I got so far is low 14.6 high 16.8. I did run with ac some of the time. Sound about right? I don't have a heavy foot, but not babying either.What do others get-I know lots of variables ( manual trans, different axle ratios,tires, 4-6 cyl engines, etc). just wondering. BTW engine idle up a little since tune-up, so it may be a little more efficent-maybe best MPG I am gonna see?.
I average 18 mpg in my stock 97 tj with 115k miles. I have a manual transmission and a 4.0l motor. I drive good mix of highway and city. I dont go over 65 often though.

Also I run regular gas. Primium, as I understand it, burns cleaner in your motor which is why WVs and BMWs need it due to their precision components but premium also burns faster. Jeeps are not precision. Running regular gas will probably get you from 16 to 18.
 

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Wow mine seem to be on the low side... I'm averaging 12-14mpg around town. Haven't had it on the freeway much as I'm chasing down a death wobble issue. If you're getting 14-16mpg I'd call that good!
 

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I average 18 mpg in my stock 97 tj with 115k miles. I have a manual transmission and a 4.0l motor. I drive good mix of highway and city. I dont go over 65 often though.

Also I run regular gas. Primium, as I understand it, burns cleaner in your motor which is why WVs and BMWs need it due to their precision components but premium also burns faster. Jeeps are not precision. Running regular gas will probably get you from 16 to 18.
You are correct in that regular 87 is recommended for TJs. High end cars need higher octane because they compress the air and fuel more than the 4.0l does. The lower octane fuel is easier to light, so the higher compression motors have fuel pre ignition issues. That's why they need the higher octane which is harder to light.
 

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FYI - Mid grade and premium are stupid terms. The grades of gas have nothing to do with being "better" quality. We have different Octane levels. The higher the octane, the more resistance to premature detonation. Higher compression engines (VW) need High Octane to reduce knocking which would freak out the knock sensor and make the car run crappy and possibly damage the engine.
 

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FYI - Mid grade and premium are stupid terms. The grades of gas have nothing to do with being "better" quality. We have different Octane levels. The higher the octane, the more resistance to premature detonation. Higher compression engines (VW) need High Octane to reduce knocking which would freak out the knock sensor and make the car run crappy and possibly damage the engine.
:thumb:
 
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