4.0L I6 Jeep

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Originally Posted By: MrRPM

my jeep is a 2001, can you give more information about these piston skirt failures? is it due to lack of lubrication or [censored] pistons?




Piston skirt failure is NOT common on a 4.0. It does happen, but its still very rare and I personally think it comes from over-revving while mudding, generally.

The bigger thing you HAVE to watch for on a 2000 or 2001 is the "331" head casting, which is prone to cracking between cylinder 3 and 4 under the valve cover. It won't lose compression because the crack doesn't go into the combustion chamber, it just gets water in the oil and then ruins the main bearings. If you have a 2000 or 2001, then DO NOT ever let it overheat! Keep an extra watchful eye on cooling system components and if it ever starts to run hot, SHUT DOWN faster than you would most iron-head engines. Watch the coolant reservoir really close (I check mine at least once a week) and if you notice coolant disappearing, have the oil analyzed to see if there's coolant in it.
 
Originally Posted By: 440Magnum
Originally Posted By: MrRPM

my jeep is a 2001, can you give more information about these piston skirt failures? is it due to lack of lubrication or [censored] pistons?




Piston skirt failure is NOT common on a 4.0. It does happen, but its still very rare and I personally think it comes from over-revving while mudding, generally.

The bigger thing you HAVE to watch for on a 2000 or 2001 is the "331" head casting, which is prone to cracking between cylinder 3 and 4 under the valve cover. It won't lose compression because the crack doesn't go into the combustion chamber, it just gets water in the oil and then ruins the main bearings. If you have a 2000 or 2001, then DO NOT ever let it overheat! Keep an extra watchful eye on cooling system components and if it ever starts to run hot, SHUT DOWN faster than you would most iron-head engines. Watch the coolant reservoir really close (I check mine at least once a week) and if you notice coolant disappearing, have the oil analyzed to see if there's coolant in it.



I agree, those that say happent to 4.0L is those that rev the [censored] out off these 4.0l, if u want off road get a v8, v8 have a better tranmission also.

btw if the head ever crack, try get new head out off 04+
 
Originally Posted By: 440Magnum
Originally Posted By: 84zmyfavorite
Ive got 6 Cherokees, 4 of have the 4.0, and none of them sound like a tractor.


I think they sound like tractors (specifically like an Oliver 1600). But then I mean that as a compliment- an Oliver 1600 was smooth as silk, purred quietly at idle, and had torque to reverse the earth's rotation.

:-)


I say sound like tractor or small desiel engine, but I only heard the lifter noise when I roll my window down, if window up, I dont heard a thing, just the smooth engine sound.
 
jeeps are e breed of tere own with maintenance, yea jeeps like there 02 sensors replaced before failure same with fuel filter.
when I bring home a "new to me" jeep I always do;
trans filter, fluid (no flush if over 60k), than evry 60K
F/R diffs ,than every 30k or so
Oil n filter
TC, than again every 30k or so
Coolant, than every 2 years or so
if it's @ 100k than PS fluid, Brake fluid, Fuel filter, 02 snesors, HM oil

as far as fluids go.

Originally Posted By: MrRPM
thanks for the info on the main seal, also i have already done the tranny filter service. when I bought the jeep i did everything, i love to do maintenance and it makes me feel better knowing im doing everything I can to make my jeep last.

should O2 sensors be replaced even if there are no problems? I figured once the jeep throws on the engine light is when its time to replace them (if the CEL is for the o2 sensors)

my jeep is a 2001, can you give more information about these piston skirt failures? is it due to lack of lubrication or [censored] pistons?
 
Originally Posted By: wsar10
jeeps are e breed of tere own with maintenance, yea jeeps like there 02 sensors replaced before failure same with fuel filter.
when I bring home a "new to me" jeep I always do;
trans filter, fluid (no flush if over 60k), than evry 60K
F/R diffs ,than every 30k or so
Oil n filter
TC, than again every 30k or so
Coolant, than every 2 years or so
if it's @ 100k than PS fluid, Brake fluid, Fuel filter, 02 snesors, HM oil

as far as fluids go.

Originally Posted By: MrRPM
thanks for the info on the main seal, also i have already done the tranny filter service. when I bought the jeep i did everything, i love to do maintenance and it makes me feel better knowing im doing everything I can to make my jeep last.

should O2 sensors be replaced even if there are no problems? I figured once the jeep throws on the engine light is when its time to replace them (if the CEL is for the o2 sensors)

my jeep is a 2001, can you give more information about these piston skirt failures? is it due to lack of lubrication or [censored] pistons?





Good points. I too did all of these in additions to the gaskets for each.

Wheel bearings tend squeal also.
 
Originally Posted By: jdoria
What about Amsoil Heavy Duty Diesel Oil in a 10W-30? It was recommeneded to me and Im going to try some after the Rotella is out of the engine.

AMSOIL is way overpriced for me, I do roughly 4k mi OCI's and I'm not one to wait around for my oil to come in the mail, overpriced to start with + S&H= forget it !

The rotella is cheaper and just as good.


disclosure;
I'm not by any means saying AMSOIL is not good oil
 
Last edited:
Originally Posted By: wsar10
Originally Posted By: jdoria
What about Amsoil Heavy Duty Diesel Oil in a 10W-30? It was recommeneded to me and Im going to try some after the Rotella is out of the engine.

AMSOIL is way overpriced for me, I do roughly 4k mi OCI's and I'm not one to wait around for my oil to come in the mail, overpriced to start with + S&H= forget it !

The rotella is cheaper and just as good.


disclosure;
I'm not by any means saying AMSOIL is not good oil


Amen brother, not big fan of amsoils, I want something that I can get right away, any time anyw where I want.
 
Originally Posted By: MetalSlug

btw if the head ever crack, try get new head out off 04+


Well, year matters less than whether it has the letters "TUPY" cast into it near where the number ending in "331" is cast. That identifies the "fixed" head casting.

The other and more reliable alternative is to go aftermarket. Most of the Jeep forums recommend Alabama Cylinder Head. Readily available, great price, no cracking flaw.
 
Alabama Cylinder Heads price for a New, Improved 4.0 head is $539 to your front door. Im thinking many 4.0s have been overreved not just in mud, but on pavement, gravel, rock, fireroads, Highways, etc. Knowing the sounds that a 4.0 makes when piston skirts get worn, listening to Many 4.0s run, I believe it IS common for piston skirts to wear in Jeep 4.0s.
 
Originally Posted By: 84zmyfavorite
Alabama Cylinder Heads price for a New, Improved 4.0 head is $539 to your front door. Im thinking many 4.0s have been overreved not just in mud, but on pavement, gravel, rock, fireroads, Highways, etc. Knowing the sounds that a 4.0 makes when piston skirts get worn, listening to Many 4.0s run, I believe it IS common for piston skirts to wear in Jeep 4.0s.

it's only common for a few years of production,
But I 100% agree about the overreving it's called a 4.slow for a reason and guys want it to have the take off and pickup of a V8, the 4.0 shine in low end torque and durability not getting upto hi-weay speeds in 3.5 sec.
 
Originally Posted By: wsar10

it's only common for a few years of production,
But I 100% agree about the overreving it's called a 4.slow for a reason and guys want it to have the take off and pickup of a V8, the 4.0 shine in low end torque and durability not getting upto hi-weay speeds in 3.5 sec.


You have some typos in there. The most important one is "... not getting up to highway speeds in 3.5 sec." You have an extra decimal point. It should read "...up to highway speeds in 35 sec."

:-)

Actually, the 4.0 XJ (Cherokee) was considered surprisingly fast for its day... but then its day started in 1984 when pickup trucks were quicker than many "sports" cars. I LOVE my 4.0s, but I do have to re-adjust my whole attitude when driving them. Its made me a calmer person, frankly. ;-)
 
Originally Posted By: 440Magnum
Originally Posted By: wsar10

it's only common for a few years of production,
But I 100% agree about the overreving it's called a 4.slow for a reason and guys want it to have the take off and pickup of a V8, the 4.0 shine in low end torque and durability not getting upto hi-weay speeds in 3.5 sec.


You have some typos in there. The most important one is "... not getting up to highway speeds in 3.5 sec." You have an extra decimal point. It should read "...up to highway speeds in 35 sec."

:-)

Actually, the 4.0 XJ (Cherokee) was considered surprisingly fast for its day... but then its day started in 1984 when pickup trucks were quicker than many "sports" cars. I LOVE my 4.0s, but I do have to re-adjust my whole attitude when driving them. Its made me a calmer person, frankly. ;-)





I agree. The 4.0L (especially the high output) cherokees were considered quick for their day. The reason is the lighter unibody yields a good power to weight ratio. In modern standards the 4.0 is probably not considered fast, but the torque curve makes it very pleasing to drive. My dad had a '99 WJ Grand Cherokee with the 4.7L V8. While the V8 has more power, I enjoyed driving the 4.0L around town. The flat torque curve means you don't have to really get on the gas much to accelerate from a stop. The V8 has more power but it is top end power.

Edit: I'd also like to add that I have an Alabama Head on my jeep and it has been great so far. Being a broke college student who uses the Jeep to commute to school I replaced it as a preventative measure while I had the money and time. I'd rather rest easy at night than have to catch rides to campus while my jeep gets repaired if the head were to crack.
 
Last edited:
Originally Posted By: wsar10
jeeps are e breed of tere own with maintenance, yea jeeps like there 02 sensors replaced before failure same with fuel filter.
when I bring home a "new to me" jeep I always do;
trans filter, fluid (no flush if over 60k), than evry 60K
F/R diffs ,than every 30k or so
Oil n filter
TC, than again every 30k or so
Coolant, than every 2 years or so
if it's @ 100k than PS fluid, Brake fluid, Fuel filter, 02 snesors, HM oil

as far as fluids go.


I have done all of these except PS fluid (i have a leak so its soon going to be changed when i rebuild the gearbox) brake fluid was flushed 3 days ago, fuel filter in wranglers appear to not need a changing according to info i have found, from what i understand they should not need to be changed if proper fuel has been used. I may need to look this up again, but i do have a whole new fuel pump assembly and i wonder if the fuel filter was changed...
I have not done 02 sensors, but as you said you do that at 100k, im at 75k.
also, what is HM oil?

thanks
 
I've had quite a few Jeeps recently, I have an 11 Overland 5.7. I've recently had an 07 SRT-8, 07 Limited 4.7, 06 Liberty 3.7, 06 Wrangler Sahara 3.7 and loved them all. For some reason, I always have a Jeep or two in the driveway.

I now drive a few new cars in the 300-500hp range from the factory now and do think this old Jeep is quite a car. Feels fast, tracks straight, may last a lifetime. I just got into it and will keep restoring them. I took my 98 out this AM for a "run the MMO through the gas tank" run up 684. At 70 mph was completely enjoyable.

But the thing gets too good an MPG, I only burned though a quarter tank before I had to go home.
 
Originally Posted By: 440Magnum


The bigger thing you HAVE to watch for on a 2000 or 2001 is the "331" head casting, which is prone to cracking between cylinder 3 and 4 under the valve cover. It won't lose compression because the crack doesn't go into the combustion chamber, it just gets water in the oil and then ruins the main bearings. If you have a 2000 or 2001, then DO NOT ever let it overheat! Keep an extra watchful eye on cooling system components and if it ever starts to run hot, SHUT DOWN faster than you would most iron-head engines. Watch the coolant reservoir really close (I check mine at least once a week) and if you notice coolant disappearing, have the oil analyzed to see if there's coolant in it.



Some 99s also; an online search for "0331 head" will turn up a whole lot of documentation.
 
Originally Posted By: jeepman3071

Originally Posted By: 440Magnum

Actually, the 4.0 XJ (Cherokee) was considered surprisingly fast for its day... but then its day started in 1984 when pickup trucks were quicker than many "sports" cars. I LOVE my 4.0s, but I do have to re-adjust my whole attitude when driving them. Its made me a calmer person, frankly. ;-)


I agree. The 4.0L (especially the high output) cherokees were considered quick for their day. The reason is the lighter unibody yields a good power to weight ratio. ...




When first introduced, the 4.0 had more power than many V8s on the road, and were faster than many police cars.
[Source: http://www.allpar.com/mopar/40.html]
 
People say the 4.0 is a strong engine but now I read they are all cracking lol

Ill keep an eye on coolant level and oil level
 
Originally Posted By: MrRPM
People say the 4.0 is a strong engine but now I read they are all cracking lol

Ill keep an eye on coolant level and oil level


The 4.0 engine platform is solid, it's only the "0331" head from 2000-2001 XJ's and 1999-2001 TJ/WJ's that may have issues.
 
well Ill have to check my casting number, it is 10 years old. maybe in its lifetime someone already changed the head out.
i have a warranty for the next year...how can i make it crack without damaging anything else? hahahaha jk

also I feel i could swap the head out myself so if the time comes its ok...can anyone say port N polish? LOL
 
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