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Old 02-16-2012, 05:01 PM   #1
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2.5L or 4.0L please help

I am buying a jeep soon but i dont know which engine is good please help and how long does the gas tank last before refueling.

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Old 02-16-2012, 05:05 PM   #2
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Ether isnt going to last long before refueling, but the 4.0 will have a little more oomph for hills and wind....

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Old 02-16-2012, 05:11 PM   #3
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If you want to lift and put big tires get a 4.0. In my opinion it's one of the best engines made by Chrysler. I had a 2.5 Before my 4.0 (tjs tho but pretty much same engines). and after I put 33's without regearing it wouldn't move. I couldn't be happier with my 4.0 and you can go around 200 miles a tank usually more if your light on the gas. And depending which tank size you have because I'm not sure about yjs but tjs come with a 15 or 19 gallon.
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Old 02-16-2012, 05:50 PM   #4
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FYI..... if you are worried about EITHER gas mileage OR miles per tank.....skip the Jeep....ANY Jeep.......or... for THAT matter... any 4WD.....
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Old 02-16-2012, 05:54 PM   #5
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Originally Posted by H8-roads
If you want to lift and put big tires get a 4.0. In my opinion it's one of the best engines made by Chrysler.
gm designed the 2.5 and 4.0. I agree with H8-roads if you lift it and put bigger tires get the 4.0. That is, unless you like being passed by school buses, and trying to find the best downhill route.
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Old 02-16-2012, 06:01 PM   #6
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I have both and they get the same mpg. I definitely prefer the 4.0
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Old 02-16-2012, 06:07 PM   #7
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i have a 2.5l with 33/12.5/15r and thats the biggest i can go otherwise it wont pull. unless i change the gear ratio and stuff like that. thats why im swapping my motor to the 4.0 or a v8 but if ur gonna buy a jeep i would just go for a 4.0l def a better choice
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Old 02-16-2012, 06:20 PM   #8
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I am running a donor rear axle underneath my Jeep right now, geared to 3.55. Essentially, it's the same as running 33" tires, but I'm on 29" tires (stock gears are 4.10 with the 4 cylinder).

If I want to get up and go it will absolutely push me around. However, since I'm besting 14mpg feather footing it, I don't do that. People think the 2.5L engine is a gutless junk pile, and they're absolutely full of sh*t. The 2.5L is no 4.0, but it will keep up. Even my crappy gearing I can keep up with both of my buddies 4.0 Jeeps on the highway, cruising at 70mph and 3000rpm.

Does it pull as hard up hills? No, definitely not, but neither will a 4.0 with 33" tires. RE-GEARING is what you want to do if you intend to run larger tires on the road, that will keep the power going to the ground about the same as stock.

FWIW, offroad they both perform the same, granted you are geared correctly. You will be happy with either, and of course there is plenty of things you can do to a 2.5L engine (TBI or MPFI) to get more power out of it. Anywhere from a modest 8-10hp power increase all the way up to +45hp.

Gas mileage varies from 10-20mpg, either 4 or 6 cylinder, depends entirely on the type of driver you are as well as the setup underneath. Your engines running condition can play a part too. You can expect to get around 200 miles per tank of gas (15 gallon is closer to 180ish and 20 gallon is around 230ish, stock of course), but like others have mentioned you don't buy a Jeep because you want something that's fuel efficient. We use the gas them hybrids don't
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Old 02-16-2012, 06:21 PM   #9
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Me and my friend both have YJ's. He has the 2.5 and I have the 4.0.......He hates me....lol
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Old 02-16-2012, 06:22 PM   #10
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completely agree with u Xpress!
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Old 02-16-2012, 06:41 PM   #11
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go ahead and buy the 4.0.(about)same gas milage and more power.you will be happier.i hate my 2.5 and im in the process of swapping to 4.0
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Old 02-16-2012, 08:56 PM   #12
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Oh well , you know the Guys that say it's not how big, but how you use it, well old racier say you can't bet C.I.D., your do the math!
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Old 02-16-2012, 10:35 PM   #13
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Thank you all for your help you guys are the best. I am definitely buying a 4.0L haha as xpress said "we use the gas them hybirds dont".
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Old 02-16-2012, 11:01 PM   #14
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my 2.5 YJ does just fine for what I use it for. If you want speed and/or gas mileage buy something different.

the 2.5 pulls just fine up hills, you just have to learn how to drive it!

BTW I just went from 31" to 33" NO difference.

I was getting 16.9999mpg before tires.

I believe all YJ's have a 20 gal tank, some are just "modified" at the factory to 16 gal.

look it up, easy mod.
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Old 02-17-2012, 08:10 AM   #15
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Go 2.5. It's just all around better haha...in my opinion. They are no powerhouses but I had the 4.0 in my old jeep and that thing wasn't puttin me back in the seat either, and it bogged on hills. I'm just a fan of the four bangers. First hand I have seen them go where the sixes and v8s haven't.
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Old 02-17-2012, 09:22 AM   #16
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The 2.5 has decent torque for trail riding. Wasn't great for me for driving on the road. Will last a long time if taken care of.

4.0 has good torque for trail riding and is tolerable on the road. Will last a long time if taken care of.

Gas mileage I got from the two was pretty much the same.

Main thing missing from this thread is which would be better overall. Adding in that the 4.0 comes with the AX-15 vs the AX-5 seals the deal every time for me personally.
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Old 02-17-2012, 12:26 PM   #17
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^My Ax5 is working fine still. As long as you drive it like a Jeep and not a sports car, then it will put up with you just fine.

The issue with the 2.5L engine is the powerband it makes. It really does need a different cam and head to change that torque range to make it come in from a low RPM all the way up to 3000rpm then go down from there, then it would pull awesome. Instead it does it from about 2500pm to 3500rpm.
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Old 02-17-2012, 05:07 PM   #18
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I'm getting the same mileage with my 4.0 that I was with the 2.5. I don't have to be concerned with rush hour traffic now. It also still moves pretty well even with the 3.5" lift and 33" tires. It's got 3.73 gears since it was formerly a 2.5 auto though.

I generally see about 225 miles per tank...20 gallon mod.
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Old 02-17-2012, 10:30 PM   #19
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Forget about the 2.5 I own one and it is a joke if you plan to drive on the road much. The 4.0 is much more powerful and has much more torque. I own 5 Jeeps 4 have 4.0's, and I will never buy another with a 2.5 in it.

The 2.5 does great off road and is very capable in low range, and that is good enough for me as I spend most of my time in mine off road. However, if you plan to run anything bigger than 235/75/15's I would look for a manual 4.0.
I have even tried to run the crap out of mine (4-5,000 rpm's) like I was racing it, and even though it was little better, you just can't drive something around like that all the time.
My last trail rig 4.0 had over 350,000 miles on it whn I sold it and is still running good. I have never seen a 2.5 go that long. And remember the 4.2's have more torque that the 2.5 but not more horsepower
I know some people say "mine can run with the 4.0's"
Do the math, look at the #'s. I wish my 2.5 would run with the 4.0, but eeennnnhhh......denied

Engine specs below..........................................
2.5L I4 TBI (fuel injected) - 121 hp @ 5000 rpm, 135 ftlb @ 3500 rpm - used in '87-'90
2.5L I4 MPI (multi-port injection) - 130 hp @ 5250 rpm, 139 ft lb @ 3250 rpm - used in '91-'95

4.2L I6 Carburated AMC 258 - 112 hp @ 3200 rpm, 210 ft lb @ 2000 - used in '87-'90

4.0L I6 MPI AMC 242 "Power Tech HO" (High Output) - 190 hp @ 4750 rpm, 220 ft lb @ 4,000 rpm - used in '91-'95
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Old 02-17-2012, 10:50 PM   #20
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that mpi 2.5 130 hp @ 5250 rpm wow!mine dont see much more than 3500 rpm and it sounds like it is going to blow up. so that around 100 hp @3500-3700 rpm.dang no wonder the 2.5 dont have no power
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Old 02-17-2012, 11:55 PM   #21
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Someone is FOS, again. I'm on 235/75's with a 3.55 donor rear end, and even then it pulls perfectly fine on highways and around town- same as 33" tires, just not.

YOU DON'T NEED A 6 CYLINDER FOR ROAD USE. End of story, MANY Jeepers DD their 2.5's perfectly fine, even with tires all the way up to 33". Tired of hearing people bash the 2.5L, it's a great TOUGH little engine, even I can hold 65mph down the highways perfectly fine. If I need to speed up then I can, but the speed limit is 65mph around here. And yes, even I can pass buses going uphill easily- that's a 7% grade for 4 miles.

Sure, a 6 cylinder is nice to have, because it pulls harder than the 4 cylinder does, but it's not necessary, offroad or onroad. If you need to be able to hold 75mph down the highways, then you need to move on from your Jeep to something made to go fast. A Jeep is not made to go fast.
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Old 02-18-2012, 12:10 AM   #22
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theres actually a discussion goin on here??? theres no question bout it, 4.0 is the way to go!!! even with a 4.0 i was boggin down on slight slopes up hill!!! till i regeared!! yu will regret a buying a 2.5L i promise you that......
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Old 02-18-2012, 12:12 AM   #23
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p.s i made my jeep to go fast and anywhere else it would wanna go!!! hehe
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Old 02-18-2012, 12:24 AM   #24
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Someone is FOS, again. I'm on 235/75's with a 3.55 donor rear end, and even then it pulls perfectly fine on highways and around town- same as 33" tires, just not.

YOU DON'T NEED A 6 CYLINDER FOR ROAD USE. End of story, MANY Jeepers DD their 2.5's perfectly fine, even with tires all the way up to 33". Tired of hearing people bash the 2.5L, it's a great TOUGH little engine, even I can hold 65mph down the highways perfectly fine. If I need to speed up then I can, but the speed limit is 65mph around here. And yes, even I can pass buses going uphill easily- that's a 7% grade for 4 miles.

Sure, a 6 cylinder is nice to have, because it pulls harder than the 4 cylinder does, but it's not necessary, offroad or onroad. If you need to be able to hold 75mph down the highways, then you need to move on from your Jeep to something made to go fast. A Jeep is not made to go fast.
I have a 4.0 in my YJ and my father has a 2.5 in his TJ. I love my 4.0 and I give him hell about having a smaller engine than me but truth be told his lil 2.5 went everywhere I did.. and he didn't have to be winched out. Damn ruts/tree roots..
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Old 02-18-2012, 12:25 AM   #25
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Xpress come on man. (all this is in good expression, I'm not starting a problem) No one is bashing. I'm not trying to single you out alone, but if the 2.5 was so great and powerful why have I and alot of other people swapped them. I drove to the beach (4 hours) and I swore I would never do out again with the 4 cyl. I was hoping that someone would see me struggling trying to keep up with traffic and just let me throw a chain around their bumper and help pull me. I got passed by a school bus, and decided to draft a semi for about 2 hours. I hated the jeep after that. Even with 4.88 gears with 33s. I did the 4.0 swap and went back down to 4.10s and now I drive the jeep everywhere like a normal person. Even 9-10 hour trips to ohio. And I don't even think about going to slow, or what if I hit a big hill. I can even keep it in fifth gear and definitely don't worry about the snap ring popping off anymore. As implied before, I'm not downing anything of yours. The question was basically what do you prefer. With that said, if it made no difference in cost, would you pick your jeep with the 2.5 or the 4.0?
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Old 02-18-2012, 12:31 AM   #26
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And for the quote, "A Jeep is not made to go fast." I totally agree! But I think it should atleast be able to keep up with traffic. 4th gear to the floor on a slight incline with 4.88 and 33s, still getting passed by everyone, I call that a road hazard.
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Old 02-18-2012, 07:28 AM   #27
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And for the quote, "A Jeep is not made to go fast." I totally agree! But I think it should atleast be able to keep up with traffic. 4th gear to the floor on a slight incline with 4.88 and 33s, still getting passed by everyone, I call that a road hazard.
Well said.

I am bashing the 2.5 for road use. They just have to work too hard. They don't get better mileage, sometimes worse, and it isn't advisable to try to tow anything of any real weight with it. It isn't about speed, but on the road they are just too weak for "normal" driving with bigger tires. You can only re-gear to 4.88's on stock axles
If someone asks advice (which is what this post is about) I try to tell them as much as I can about something I know about. I own a 2.5 it is only good for off-road IMO. AS far as you driving with 3.55 gears and 235's you should be able to I have a 4.0 with 3.55 gears and 33's and it pulls much better than my 2.5 with 4.10's and 33's on the road.
I am just trying to give someone an honest answer from experiences that I have had on my own vehicles.
As far as a 2.5 "keeping up" off road they do really great, on the road after 2nd gear it is over in comparison. This is the truth not a pissing contest.
I have owned a lot of Jeeps and the only engine I have been disappointed with is the 2.5. And keep in mind I am not trying to drive fast the 2.5 just will not pull like the 4.0, that is the issue here
If I did more street driving I would sell mine or do a motor swap but for my use (80% offroad) mine is great for what I use it for.
In summary, the 2.5 can run 65-75 mph although it will not do it without a lot of effort. I didn't get mine to run the highway. I got mine to wheel.
The 4.0 gets around the same mileage(sometimes better), twice the torque, 1.5 times the HP, and better tranny. There is nothing left to really say except some people are faithful to the little 4 banger and that is fine. I am just putting what I know out there for someone that should know all the facts
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Old 02-18-2012, 09:08 PM   #28
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1995 Jeep 2.5L with just a throttle body spacer (can tell a difference with it on hwy). I get 300 miles to a tank city and hwy with the 20 gal conversion. Will soon be doing a electric fan and a 4.0 throttle body conversion.
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Old 02-18-2012, 10:01 PM   #29
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I am buying a jeep soon but i dont know which engine is good please help and how long does the gas tank last before refueling.
So, I guess the OP should be more specific. What do you want or expect from a jeep. Then maybe we can give you better advice?
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Old 02-18-2012, 11:25 PM   #30
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Well said.

The 4.0 gets around the same mileage(sometimes better), twice the torque, 1.5 times the HP, and better tranny. There is nothing left to really say except some people are faithful to the little 4 banger and that is fine. I am just putting what I know out there for someone that should know all the facts
thats my point.who with the 2.5 hasent wanted the first sentence

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