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What gets better mpg 4.0 or 2.5?

104K views 75 replies 39 participants last post by  DirtyRob 
#1 ·
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,
 
#68 ·
Ahhh but do you really win driving a Prius ?
 
#7 ·
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
 
#10 ·
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:nonono: Do you think the 2.5's mpg start to drop more than the 4.0 the bigger the tires get? Thanks Nathan,:thumb:
 
#32 ·
So is there any reason to get the 4 banger if the sixes are getting the same?
Cost. Not of gas but of the Jeep itself. I've found the 4.0 runs about 10-15% more to buy regardless of the year.

I kick my own butt for not having a 4.0.
 
#11 ·
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 ;)
 
#23 ·
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.
 
#12 ·
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
 
#14 ·
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..
 
#18 ·
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}.:nonono: 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.
 
#15 ·
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!:thumb:
 
#16 ·
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
 
#19 ·
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.
 
#22 ·
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.
 
#27 ·
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?
 
#29 ·
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.


 
#30 ·
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.
 
#37 ·
Too many factors. Mine was abused and treated poorly, so therefore at 100,900 miles it is in need of a rebuild. Blowing oil mainly.. However it does run strong still. A well cared for 2.5L will last over 400,000 miles easily. Maybe go until the odometer rolls over.

As for trading it for a bigger engine... No, I will not. I'm too attached to this thing just to give it up. Too much sentimental value in it. However I wouldn't mind having another Jeep with a 4.0 in it. I would absolutely buy another 2.5L Jeep though, they're so readily available around here and for cheap that it's too hard NOT to buy one to build up. But a 4.0 first.
 
#34 ·
I'm seriously considering trading my 2.5L for a 5.7L :punk:
 
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