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Old 03-05-2012, 07:55 AM   #1
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Why would the 2.5 throw a rod

This thread is intended to try and help those Jeepers out there that have the 2.5L from throwing a rod and losing an engine. I hope those that take some kind of pleasure in bashing the 2.5 can stay at home. Such comments are neither wanted nor needed. It ain't helpful.

Apparently there is some tendency for the 2.5L to throw a rod, specifically #2. IBUILDEMBIG as published some photos showing just that and has seen instances.

Typically this would not happen on any well maintained engine if run within its rpm limits (basically below redline), even over extended periods. Possibly, if not designed properly, premature wear could spin a bearing and cause it.

PLEASE keep this thread informative only such that we MIGHT be able to save a Jeeper or 2 from losing an engine. I would hope to find out what caused it and what could avoid it (besides some juvenile smartass response to "replace it with something bigger").

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Old 03-05-2012, 11:33 AM   #2
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what years are we talking about? my 2.5L is a 99 with 165,000 and i want it to see 250,000! is it real common or more of a used abused stuff...I got it at 153,000 so who knows what its seen (new plugs, wires and oil yesterday by me though!)

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Old 03-05-2012, 01:33 PM   #3
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that what trying to figure out

That is what I am trying to figure out and see if there is something preventative to do.
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Old 03-05-2012, 06:23 PM   #4
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I didnt know this was a known problem but my old 99 2.5 had a rebuilt engine in it when i bought it. It was installed at 90,000 miles cause the previous engine threw a rod...i just figured the previous owner over revved the old engine or something
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Old 03-05-2012, 07:51 PM   #5
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Like I said before I worked at dodge chrysler jeep dealership as a technician for two years. And the four cyilnders like to throw rods/spin bearings I think the problem is the 2.5 is way under powered for the wrangler and you have to rev it to heven just to get moving, the 4.0 has a easy life compared to a 2.5.
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Old 03-05-2012, 08:33 PM   #6
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first blush

So, at first blush it could be a bad/spun bearing problem. Wonder if that could be from lack of maintenance (oil changes) or a weak design. Certainly the 2.5 runs at a little higher rpm, but nothing approaching rod throwing rpms, unless there is some other underlying issue, like poor oil.
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Old 03-05-2012, 08:45 PM   #7
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the 2.5 is a very good engine and more than an adequate means of power in a jeep, running the hell out of it with little or no maintainance could certainly throw a rod and this could happen with any engine of any size, just because its a 2.5 doesn't mean that it is prone to slinging a rod. Take care of it and it will take care of you.
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Old 03-06-2012, 10:29 PM   #8
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The 2.5 is a good engine, but i definitely would NOT say its adequate power for a wrangler. It takes A LOT to get a wrangler with a 2.5 up to speed on the highway and up steep hills...you really have to rev that thing up to get it to go. Around town and off road it can run all day with plenty of adequate power, but if you do a lot of highway driving or live in hilly terrain that engine really has to work hard to keep up and i could see how it could take a beating from being revved so high.

Still didnt know this was a known problem though, interesting...
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Old 03-08-2012, 10:58 AM   #9
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Dirty oil versus clean oil shouldn't make a difference.


*Standing on the accelerator without a load (in neutral or with the clutch pressed) can frag an engine.


*A gross overrev (downshift or downhill) can also frag an engine.



Imagine a Jeep rolling with 33/35 inch tires going 70 mph downhill, and a driver that tosses the little 4-cylinder engine into 3rd to try to slow down. Something has got to pop.


Dirty oil, really? LOL.



Too small, LOL.


If my 5.7 Hemi can move my 7,000lb truck with a 10,000lb trailer, then the little 2.4/2.5 Jeep engine can move a 3,500lb Wrangler just fine.






Catastrophic mechanical damage, characterized here as an overload separation of a connecting rod, is infinitely more likely to be the result of a peak stress that exceeds the properties of the connecting rod material and design... than it is dirty oil or a heavy vehicle.


Your connecting rods reciprocate. This means they change direction. As speeds increase, the energy that must be redirected each stroke increases at the speed^2. (squared). It's an exponential function.

The transmission and tires, u-joints, etc, all rotate. They also generate a lot of centrifugal force, but those components don't change direction 50 or 100 times a second, so they're lass apt to grenade.



If the Wrangler were "too heavy" for the 4-cylinder, they'd be detonating in dealership lots. With the engine doing 1,000s of RPM, you'd know almost instantly.

The fact that they go 60K, 70K, etc. before grenading, with metal fragments exiting the crankcase, indicates they application is fine.

You could mount a 2.5L in an F-350 and it would do fine with the proper gear reduction and reasonable top-speed expectations.

The problem with the "thrown rod" is overrev with no load, or worse, a load that is racing the engine over redline.


The 4.0L Wranglers would be less prone to the overrev because they have more internal inertia, or "engine braking". If you get too aggressive downshifting with the 4.0L, the engine is probably more apt to overpower the clutch or lock-up the tires... versus the 2.4/2.5 which just gets revved to the moon. The 4.0L Wrangler weighs basically the same as the 2.4/2.5, and using the Jeeps own weight to cause an overrev would be tougher with the bigger engine.


IF anyone wants a demonstration, PM me and loan me your Wrangler.


By the way, I'm loving this 22/23 mpg right now. Who said I'd be sorry I bought the 4-cyl 6-speed?
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Old 03-08-2012, 11:21 AM   #10
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I call it the death rattle and can happen on a 4.0 also (mine did). Main bearings go. When you first start it you here a rattle in the lower end put shortly afterwards the noise stops. You can also hear the warning signs at high rpm when doing a climb. Drop the pan end see if you can wiggle the bottom of the rods, if so do a rebuild.

Also if you do water crossings or play in water and come out the other side with your engine popping and sputtering or it dies completely that can cause weakening of the rods even if you don't have a full hydrolock.
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Old 03-08-2012, 12:50 PM   #11
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Quote:
Originally Posted by ballistx
If my 5.7 Hemi can move my 7,000lb truck with a 10,000lb trailer, then the little 2.4/2.5 Jeep engine can move a 3,500lb Wrangler just fine.
Have you driven a 2.5? Yeah it moves it, but i wouldn't quite say just fine...i'd leave it at it moves it

Haha seriously man thanks for the math and physics lesson but all i was saying is that the 2.5 is a dog and you've gotta rev it up good to get it to make adequate power to pull out into highway traffic or make it up a steep hill. Im not saying that revving it to 4-5000 rpms is gonna throw a rod, im just saying it could put more wear and tear on the engine after driving it hard for 100,000 miles.
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Old 03-08-2012, 02:01 PM   #12
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I rarely cross 3,000 on my 2.4L.

(hp/tq numbers per wiki)

2.5L performance 121/145
2.4L performance 150/165
4.0L performance 190/230



In the mid 70's the Ford 300ci I-6 only made 120hp/220tq, and those were used un F350s, school busses, and dump trucks. That is IMO the greatest gasoline engine ever created. It had a fully gear drive valvetrain, no belt or chain.


I've never driven a 2.5, and most are probably getting tired and not performing at peak. I have driven a 2.4L, and it's fine IMO. Maybe the extra 10-20% makes a decent difference.


When I bought my Wrangler, I had a specific use. I needed a vehicle I could park anywhere, fit anywhere, that could idle all day and still get 20mpg rolling to a jobsite. I recognized that it wouldn't be a race car.

I've only found my Wrangler lacking when pushing into a 50mph headwind. A couple weeks ago I came around a bend on the freeway and instantly lost speed. I thought the engine was seizing or I'd burnt a piston. I pressed the clutch and it spooled normally, then I realized I had a nasty headwind. I had to downshift into 5th to maintain speed.


Back on topic, I'd avoid overrev conditions if possible, and also high shock loads like dropping the clutch at 3,000 from a dead stop. Old gearsets and engines don't like that stuff.

A moderate load at moderate RPM is fine indefinitely.
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Old 03-08-2012, 08:39 PM   #13
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Jonny15,

Dude, the little 4 banger is more than adequate for the wranglers in an everyday driven vehicle and even for light off road driving, don't knock it. Now I certainly wouldn't want to go to the extreme with it like rock crawling or other axle breaking things like mudpit racing but my little 2.4 has plenty of spunk and I'm not a newbie to the jeep world with my first opinion about what a jeep needs as a powerplant. I've owned 3 cj-5's with v-8 engines in all of them and my son-in-laws cj-7 has the inline 6, nephew has the 6 cyl and I'm here to tell you and others don't be so judgemental to put this little motor down. It is what it is, dependable, economical, and fun to drive. After all it is a jeep and its made for people to enjoy, and the 2.4 is adequate! It's not a muscle car and was never meant to be.
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Old 03-08-2012, 09:09 PM   #14
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Quote:
Originally Posted by AKYJ View Post
Like I said before I worked at dodge chrysler jeep dealership as a technician for two years. And the four cyilnders like to throw rods/spin bearings I think the problem is the 2.5 is way under powered for the wrangler and you have to rev it to heven just to get moving, the 4.0 has a easy life compared to a 2.5.

I think this is correct. People put it in situations that cause more stress on the motor.

For example, I have a not so smart buddy that HAD a 4 cylinder in his yj with 4.10 and 33's. With him not re-gearing he put a lot more stress on the motor trying to get it moving up obstacles and so forth because he would just romp on it. I think it depends on the driver more than anything.
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Old 03-08-2012, 11:29 PM   #15
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Quote:
Originally Posted by dirt dawber
Jonny15,

Dude, the little 4 banger is more than adequate for the wranglers in an everyday driven vehicle and even for light off road driving, don't knock it. Now I certainly wouldn't want to go to the extreme with it like rock crawling or other axle breaking things like mudpit racing but my little 2.4 has plenty of spunk and I'm not a newbie to the jeep world with my first opinion about what a jeep needs as a powerplant. I've owned 3 cj-5's with v-8 engines in all of them and my son-in-laws cj-7 has the inline 6, nephew has the 6 cyl and I'm here to tell you and others don't be so judgemental to put this little motor down. It is what it is, dependable, economical, and fun to drive. After all it is a jeep and its made for people to enjoy, and the 2.4 is adequate! It's not a muscle car and was never meant to be.
Would actually say the opposite...plenty of power and torque off road and around town, not so much for an everyday highway driver. Hey i owned a 2.5 for almost 4 years, put plenty of miles on it, and drove it everyday on the highway. I havent driven a 2.4 though which is actually much more powerful than the old 2.5. Maybe thats why some of you might not get what im talking about when i say the 2.5 is a dog, cause you're driving 2.4's thst make 30 more hp and 20ft lbs more torque!! haha.

I never expected it to be a muscle car at all and i've said plenty of great things about the 2.5...but there is no comparison to the 4.0, plain and simple.

Guys we're getting off topic here...i dont know how the 2.4 even got brought into this as it was never part of the conversation, we're talking about the 2.5...

Bottom line does anyone actually know if the 2.5 is actually prone to throwing rods and if so why? Ive never even heard this before but my old jeeps previous engine threw a rod thats what i was curious/speculating the cause.
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Old 10-02-2014, 09:16 PM   #16
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what would cause that little 4 banger to sputter at 50 mph acts like the motor shuts off for a split second

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