2.5 or 4.0

[carriss]

I'm just looking for some insight on the two engines, I'm looking for a new dd because my current has a 5.0 police interceptor and does not get great mpg even though I get 21 highway and 13 to 16 on back roads and city not bad but the car is going on 20 years old and it's just time

and of course I'm a jeep person. I have been impressed with my 4.2 in my J10 and therefore I’ve been looking for a low mileage 96 to 02 wrangler with a 5 speed manual, hardtop, full doors, hardtop because my aunt has a 99 Chevy tracker and her soft top is a pain and cold in the winter and it leaks alot,


so I’m looking for the pros and cons of both engines, has anyone owned both engines and can say they liked one more than the other.

and what if any problems have showed up most common in both, Thanks for the insight ahead of time.

Picture below is my DD for now.

 

[Bounty__Hunter]

The 4.0L has been plagued with cracked exhaust manifolds up to about '01 or so until a redesign.

With stock height tires on a DD they are both good engines, but the 2.5L loses more guts when the tire size increases. If you like passing other vehicles, especially with limited sight distance, stick with the 4.0L. If power isn't a priority, either will do fine and the 2.5L is capable of a few more mpg.

I get about 16-18mpg with my 2.5L on 36" tires and 5.38 axle gears. My best was around 22mpg with 31" tires and 4.11 gears, but I've done a few engine mods to help the 4banger.

 

[carriss]

My exhaust manifold cracked on my 4.2 before my dad gave it to me I guess it's a legacy. a banks header can fix that any other flaws for the 4.0?

 

[Utah_jeepster]

The TJ line has had a few problems that have plagued it. The radiator is a known problem but when you meld plastic and metal to make a radiator...well it some times leaks around the seams.
They fixed the exhaust in 01 going to a double down tube off the manifold. Those with a single down tube have gotten cracks around the single yoke area.
The steering box worm gear some times goes faster with bigger tires but a replacement from Auto zone fixes that because of their life time warranty.
The Dana 35 is the weak link on the axles issue but that only happens with bigger tires and a heavy right foot.
The Ax-15 is a strong 5 speed with no known problems as is the NV3550 automatic. The NP 231 is a good transfer case but all non-Rubicon TJ's came with a Slip Yoke.

 

[carriss]

That's not too bad, i'm leaning to the 4.0

 

[laxpug19]

I'll give you some insight on your hard top idea. I live in mass and the winters are cold, and right now we're getting rain straight through thursday. I mean ive had some water in but thats from not shutting the door tight enough. And its not that bad, the heat in jeeps throw at you, if you didnt know. I mean warm up for about 3 min before i head out by the time at the end of the street i have hea t coming in... But if you want a hard top all summer long its all you...

 

[carriss]

What was the final decision? i found a 95 2.5 5 speed i'm going to look at it monday heres a link.

http://www.cars.com/go/search/detai...d=98681&dlid=&dgid=&amid=&cname=&aff=national

 

[Saurian]

I don't know much about the 2.5, from what I've heard, it's a quite capable engine, but doesn't necessarily have the "oomph" that some people are looking for. I've got the 4.0. I love the torque I get when my foot hits the floor, either getting on the freeway, or blasting through a mudbog.

Besides the exhaust manifold, as was mentioned, the rear main seal is known to seep on the 4.0. Mine is, and has been for a while... It doesn't even hardly spot the driveway, and I lose no oil, or at least not enough to bother worrying about it between oil changes. The only time I really notice that it's a problem is when I am hitting the gas hard, and I can smell the oil drops burning off on the exhaust pipe. So, not really a problem, but something to mention, just FYI... Hope the Jeep search goes well for you.

 

[zafirex]

Here in SC I got a used 2.5 at a fair price, mainly because the used lot couldn't move it. They said everyone wanted 4.0 to tow boats with at the beach. So if you plan on doing any towing, it sounds like the 4.0 is a better choice.

I can't get above 13 mpg with stock engine on 33x12.5 and 4 in lift (don't know the history on regearing, but have clocked the speedo and that reads correctly, so at least that change was made). The engine looked in much better shape than several other used Jeeps I looked at (all those were from Ohio or up north, had rust all over the place) and this one remained in the south. Hard to push above 55 on the highway.

Did note that after adding a throttle body spacer, K&N airtube and Rusty's airtube mount last weekend, it seems to have much better power in the low range, with quicker pickup, but no improvement at high gear/speeds. Haven't run through a tank of gas yet to see if any improvement in gas mileage. It may all be snake oil, but I had fun putting it in.

 

[carriss]

i guess if it came down to i could swap the 2.5 for a 4.0 right it would fit? i see 4.0's in junkyards alot and could get one pretty cheap, would the transmission be the same on 2.5 and a 4.0?

 

[carriss]

is the 2.5 to a 4.0 a possible bolt up install?

or do i need more parts than a 4.0 and electronics that go with it?

has anyone heard of someone doing or done it themselves?

 

[TerryMason]

p0p

 

[carriss]

Anyone own a Jeep?

 

[TwistedCU]

I like the 4.0 mated to an auto transmission. I used to be a manual trans guy but Jeep manual transmissions have not been good to me. The BA series were horrible, the AX series were the pits, and the new 6 speed is a hunk of junk. The last 5 speeds that came on TJ's were decent. They should have stuck with them.

The Automatics are all strong and reliable. The 999's to the AW4.

is the 2.5 to a 4.0 a possible bolt up install?

or do i need more parts than a 4.0 and electronics that go with it?

has anyone heard of someone doing or done it themselves?

To replace a 2.5L with a 4.0L you need to change the computer, and the transmission from the 4 banger most likely won't hold up so change that too.

 

[carriss]

So the transmissions are different from each other or is it just the clutch/fly wheel set-up,

do you know of any weak points of a 2.5 trans?

motor mounts the same?

anyone know the stock mpg average of wranglers? 2.5 and 4.0?

 

[Bounty__Hunter]

The trannies are different between the 2.5L and 4.0L, they won't interchange except for AA's new adapter for the AX15 (6cyl transmission) behind a 2.5L.

The motor mount perches are in a different location (on wranglers) and would need cut off and relocated for any engine swap.

Biggest weak point of the AX5 behind the 2.5L is the use of the wrong fluid, but same holds true for the AX15 behind the 4.2L and 4.0L. THey are strong enough to handle the power of the engines they follow.

 

[carriss]

That's what i wanted to know. Thanks, the search continues......................................................