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Old 04-16-2012, 08:42 PM   #1
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What gets better mpg 4.0 or 2.5?

I'm looking at buying a 92-95 YJ and want the best mileage possible running 31" mud tires. I drive with a light foot. I heard someone say they were getting 20 highway and 17 city with their 1993 Wrangler 4.0 running 31's. Is that common or possible? Thanks Nathan,

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Old 04-16-2012, 09:13 PM   #2
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you may not believe this but i just did the math for my 2.5 and i averaged 20 mpg with mixed highway/city. I run BFG A/T 33's...

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Old 04-16-2012, 09:14 PM   #3
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I get the same mileage with my 4.0 as I did with my 2.5.
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Old 04-16-2012, 09:19 PM   #4
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A toyota prius wins.

But you all beat me, my cj gets 11 mpg.
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Old 04-16-2012, 09:42 PM   #5
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I get the same mileage with my 4.0 as I did with my 2.5.
X2

As a jeep owner, poor fuel economy is the reality no matter what you do. It helps that my gas gauge and speedometer no longer work, now I can concentrate on having fun.
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Old 04-16-2012, 10:00 PM   #6
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I get 19-20 city with my 2.5l, never take her on the highway cause I'd get run over. LOL!
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Old 04-16-2012, 10:15 PM   #7
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my wife's stock 93 with 4.0 and auto got 19-20 on the highway but in the mid teens in town. but that was with the ac on all the time
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Old 04-16-2012, 10:48 PM   #8
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Quote:
Originally Posted by Bobinayj
X2

As a jeep owner, poor fuel economy is the reality no matter what you do. It helps that my gas gauge and speedometer no longer work, now I can concentrate on having fun.
True story.
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Old 04-16-2012, 11:04 PM   #9
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Quote:
Originally Posted by 95YamJam
I get 19-20 city with my 2.5l, never take her on the highway cause I'd get run over. LOL!
Lol I get ran over and I have the 4.0 lol. 33s and low gearing. Not so good on the highway
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Old 04-16-2012, 11:49 PM   #10
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So is there any reason to get the 4 banger if the sixes are getting the same? I know that any Jeep isn't a Prius, but with $4bucks a gallon I would like to get the best I can! My F250 gets about 8mpg so anything is a upgrade Do you think the 2.5's mpg start to drop more than the 4.0 the bigger the tires get? Thanks Nathan,
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Old 04-17-2012, 12:05 AM   #11
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The 2.5 runs at higher rpm while you could drive the 4.0 under 2K rpm if you tried. I think your theory's right, with bigger tires, the 2.5 is gonna have to work so much harder than the 4.0 to achieve the same thing. I have the 4.0 with 31s and I average about 20 mpg. Just look at all the topics people start about wanting to swap over to the 4.0, I think that's proof enough the 4.0 is better
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Old 04-17-2012, 01:03 AM   #12
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The newly adjusted ratings list the 2.5/5spd as 16/18...and the 4.0/5spd at 14/17 for fuel injected models. IMO, the 4.0 is well worth the 2mpg deficit listed around town. When it comes to freeway driving, my 4.0 has no problems getting up and maintaining 80-85mph. I don't regularly go over 70, but it's nice to be able to leave the slow lane and pass if I wanted. My 2.5 couldn't get out of the slow lane unless there was a strong tailwind and I was going downhill for an extended amount of time. 70mph was something I rarely even tried to get up to because it couldn't maintain.

I know the f250 pain . Twin tanks, 40 gallon capacity...but a 200mile range with my 88 extended cab long bed 4x4 with a 3 speed auto. Makes the yj look like a civic at the gas pumps
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Old 04-17-2012, 02:26 AM   #13
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I live in LA - where its stop sign after stop sign - light after light and I drive the jeep like its stolen... My 4 banger averages around 16-17mpg which is pretty good... I do have some bicycle tires on it though which I'm sure help.
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Old 04-17-2012, 02:17 PM   #14
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On an averaging basis... Neither engine is better than the other. They both can average the same mileage figures. I personally am seeing about 18mpg on my 2.5L with 29" tires. But then again I take my time getting up to speed, using no more than 2/5 of the gas peddle movement... It gets up and moves nicely, even on the highways.

As far as passing power... The 2.5L has it, and plenty of it. People who claim their 2.5L doesn't have it generally you will find they don't keep it tuned up on a regular schedule. Every oil change I do I also replace my distributor, rotor, air filter, and spark plugs as well as toss injector cleaner into the tank. Keep it tuned up and it will sing, I don't have issues holding 70mph on the highways, and if I need to pass someone I just drop to 4th and punch it, it gets up and moves just fine. The only time it struggles is going up LONG grades steeper than 5-6% (which is pretty steep)- there's a section of highway around here that is 3 miles long and at a 6% grade, so I have to drop to 4th and cruise the slow lane, still can manage 60 going up it though, and can pass the semis if need be..
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Old 04-17-2012, 07:04 PM   #15
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Ok, sounds like its really up to personal preference then. So what would be other factors to take into count for? Like insurance cost difference, Maintenance cost difference, how about reliability? Does one motor have more issues than the other? Thanks for all the feedback!
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Old 04-17-2012, 07:06 PM   #16
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If you plan on running 31's I say go with 2.5L. But if you plan on running 35's+ go with a 4.0. Both engines are very well built and maintaince cost is really not that different. I love my 4.7L stroker makes tiring my heavy 37's a easy. I get 18 hwy 12city
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Old 04-17-2012, 07:23 PM   #17
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I get a whole lot better gas mileage since I pulled the vent tube out of my gas tank, now instead of 15 gallons I can hold 20, man can I go a whole lot farther!
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Old 04-17-2012, 11:17 PM   #18
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Quote:
Originally Posted by Xpress View Post
On an averaging basis... Neither engine is better than the other. They both can average the same mileage figures. I personally am seeing about 18mpg on my 2.5L with 29" tires. But then again I take my time getting up to speed, using no more than 2/5 of the gas peddle movement... It gets up and moves nicely, even on the highways.

As far as passing power... The 2.5L has it, and plenty of it. People who claim their 2.5L doesn't have it generally you will find they don't keep it tuned up on a regular schedule. Every oil change I do I also replace my distributor, rotor, air filter, and spark plugs as well as toss injector cleaner into the tank. Keep it tuned up and it will sing, I don't have issues holding 70mph on the highways, and if I need to pass someone I just drop to 4th and punch it, it gets up and moves just fine. The only time it struggles is going up LONG grades steeper than 5-6% (which is pretty steep)- there's a section of highway around here that is 3 miles long and at a 6% grade, so I have to drop to 4th and cruise the slow lane, still can manage 60 going up it though, and can pass the semis if need be..

Wow, I change my oil every 5,000 miles, for the extra $50.00 spent I think I would rather the 1 to 2 mpg and have all the power you need and not have to take up for my 2.5 every time someone talks bad about them {and that's often}. Sorry no harm meant. but the 4.0 was an UPGRADE when the car sold new. The few mpg can't make up for that!
If your going to tow a 4 wheeler or pull a small boat or maybe a small utility trailer I'd get the 4.0 hands down.
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Old 04-18-2012, 12:55 AM   #19
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Nothing wrong with the 2.5L and replacing components when they wear out. Since I buy the cheap aftermarket parts I tend to replace them more often. Now if I bought OEM components and something like iridium spark plugs then I probably wouldn't be replacing them every 5,000 miles.
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Old 04-18-2012, 01:18 AM   #20
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Is the gear ratio's different between the two? Do they both run the same manual trans? Also, is there any axle difference or strength difference?
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Old 04-18-2012, 01:59 AM   #21
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So I just figured out axle ratio difference, the 2.5 is lower. So does that mean it has a lower crawl speed in 4-low? Sorry if that's a stupid question.
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Old 04-18-2012, 08:40 AM   #22
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They use the same transfer cases, but depending on the year Ge input shaft spline count is either 21 or 23. The transmissions used are different. The ax5 came behind the 2.5 and the ax15 came behind the 4.0's (there are some with the pugeot ba10/5 and a 4.2)

The ax5 has some 5th gear issues quite often. Someone about a clip coming off and thr gear sliding out of position.

If you ever plan to tow anything, the 4.0 is better suited.

The gear ratios in the axles depend on what you've got.

A 2.5 auto comes with 3.73 gears
A 2.5 manual comes with 4.10 gears
A 4.0 auto comes with 3.55 gears
A 4.0 manual comes with 3.07 gears

If you wanted to bump to 4.10 gears on your 4.0, you just find a set of 2.5 axles and throw them under. My 4.0/ax15 is running 3.73 gears since it was a former 2.5 auto. With the 33's, it is perfect. The speedo is even right.
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Old 04-18-2012, 02:51 PM   #23
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The 2.5 runs at higher rpm while you could drive the 4.0 under 2K rpm if you tried. I think your theory's right, with bigger tires, the 2.5 is gonna have to work so much harder than the 4.0 to achieve the same thing. I have the 4.0 with 31s and I average about 20 mpg. Just look at all the topics people start about wanting to swap over to the 4.0, I think that's proof enough the 4.0 is better
The 2.5l as he said has to work harder, my yj 2.5l get close to 20mpg with 33 goodyears on the highway as long as there are no hills. My rpm range at 65mph is 2,000-2,250rpm, now I also have a friend with about the same mods I have but in a 4.0l tj and he gets about the same mpg as I do on the highway but around town is worst then mine. Also gearing has a big part of mpg too. In the end if you are wheeling 4.0l or you need to force more air and fuel in the 2.5l.
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Old 04-18-2012, 03:57 PM   #24
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On an averaging basis... Neither engine is better than the other. They both can average the same mileage figures. I personally am seeing about 18mpg on my 2.5L with 29" tires. But then again I take my time getting up to speed, using no more than 2/5 of the gas peddle movement... It gets up and moves nicely, even on the highways.

As far as passing power... The 2.5L has it, and plenty of it. People who claim their 2.5L doesn't have it generally you will find they don't keep it tuned up on a regular schedule. Every oil change I do I also replace my distributor, rotor, air filter, and spark plugs as well as toss injector cleaner into the tank. Keep it tuned up and it will sing, I don't have issues holding 70mph on the highways, and if I need to pass someone I just drop to 4th and punch it, it gets up and moves just fine. The only time it struggles is going up LONG grades steeper than 5-6% (which is pretty steep)- there's a section of highway around here that is 3 miles long and at a 6% grade, so I have to drop to 4th and cruise the slow lane, still can manage 60 going up it though, and can pass the semis if need be..
Xpress,
as soon as I saw a post that covered the topic of the 2.5L, I instanly knew you would be on here defending your beloved 4 cyl to the death.
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Old 04-18-2012, 05:59 PM   #25
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The 2.5l as he said has to work harder, my yj 2.5l get close to 20mpg with 33 goodyears on the highway as long as there are no hills. My rpm range at 65mph is 2,000-2,250rpm, now I also have a friend with about the same mods I have but in a 4.0l tj and he gets about the same mpg as I do on the highway but around town is worst then mine. Also gearing has a big part of mpg too. In the end if you are wheeling 4.0l or you need to force more air and fuel in the 2.5l.
For wheeling, the 2.5L is WAY more fuel efficient, believe it or not. You have less cylinders to feed and it happily powers through regular trail obstacles at 1500rpm or less- same as the 4.0. Run both at the same RPM all day and the 2.5L will still be running miles after the 4.0 runs out of gas. The 4.0 has 2 more cylinders to feed.

The 2.5L doesn't really need to work harder. How the engine gets worked is all up to the driver, you can baby the 2.5L if you wanted to (which I do) and still manage highways perfectly fine.
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Old 04-18-2012, 06:15 PM   #26
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For wheeling, the 2.5L is WAY more fuel efficient, believe it or not. You have less cylinders to feed and it happily powers through regular trail obstacles at 1500rpm or less- same as the 4.0. Run both at the same RPM all day and the 2.5L will still be running miles after the 4.0 runs out of gas. The 4.0 has 2 more cylinders to feed.

The 2.5L doesn't really need to work harder. How the engine gets worked is all up to the driver, you can baby the 2.5L if you wanted to (which I do) and still manage highways perfectly fine.
Very true... As for highways here in CT the parkway is like hill climbing with big sharp turns. There is nothing flat or straight in this state.
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Old 04-18-2012, 07:41 PM   #27
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Well, my commute is about 20miles each way mostly flat in the middle of nowhere speed limit is 55mph but I can drive whatever. So most of my driving is nowhere near a freeway. The other issue is, most of the 4.0 are modified and look like they've been offroad, where almost all of the 2.5's are bone stock, or close to bone stock. So I was thinking of buying a 2.5 that is totally stock, and then put on it what I want. Is this a reasonable idea?
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Old 04-18-2012, 07:47 PM   #28
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By the way I'm selling a 1987 Jeep Comanche 4x4, Rebuilt 4.0, Automatic. It's in decent condition, I'm selling for $2,000. If anyone's interested I can put up pictures. I'm in Oregon.
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Old 04-18-2012, 07:57 PM   #29
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Here's some of the Jeeps I'm interested in? Let me know what you think. My budget is $4,000 or less.

This one's from a dealership for $3,995
Vehicle Details Year:
1993
VIN:
1J4FY19P9PP248168 Make:
Jeep
Stock #:
3286 Model:
Wrangler
Mileage:
126,411 Trim:
S Sport Utility
Exterior Color:
Black Enigine:
4-Cyl 2.5 Liter
Interior Color:
Black Transmission:
Manual 5-Spd



Drivetrain:
4WD








This one's private sale, $3,800.

1992 Jeep Wrangler
175,000 miles
4 cyl, 5 speed, trailer hitch
New top 2 years ago.
Runs and drives great.


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Old 04-18-2012, 09:02 PM   #30
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Go take a look at both of them and see what you think. Whichever one is in better mechanical condition and has the least amount of rust is what I would go with.

As for your reasoning, nothing about it is unreasonable. There's a lot that can be done to the 2.5L to boost its HP and torque output to give you a more comfortable ride. I commute 11.2 miles to work every day and my 2.5L powers around perfectly fine.

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