2000 Jeep XJ, PYB 10w-30 - Bad report, need help troubleshooting!

Joined
May 6, 2011
Messages
33
Location
Socal
I totally baby this Jeep (been in family since new and I'll have it forever) and keep up with all maintenance items. I replaced the cylinder head back in 2015 (30,000 miles ago). Prior to the head swap, which I did preventatively because the 4.0s in this year had heads prone to cracking, UOAs were flawless. These two UOAs were the first I've done since (kicking myself). No clue if the head has anything to do with it; it's been 7 years since the swap, but that's the only major work that's ever been done to the engine.

What's the best way to start troubleshooting other than ripping it apart? Compression test? No symptoms whatsoever, runs like a top. Unchanged oil pressure, no oil consumption, no weird noises. If it wasn't for the two bad UOAs I would say it's running perfect.
 

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cracked piston skirt?
Cracked/compromised air intake?
no other wild guesses at this time.

maybe switch to 15w40 and continue uoa?
 
What's the best way to start troubleshooting other than ripping it apart? Compression test? No symptoms whatsoever, runs like a top. Unchanged oil pressure, no oil consumption, no weird noises. If it wasn't for the two bad UOAs I would say it's running perfect.
They are talking ppm. No symptoms? Runs like a top? Unchanged oil pressure? No oil consumption? No weird noises? Just drive it like you would normally and don't concern yourself so much with a service that depends on repeat customers to stay in business.
 
It is a 4.0-if it doesn’t crack a piston, 300K is possible. If it does, find another motor & replace it (keeping your head, of course). Seems like rust claims many more than engines, my son’s ‘98 XJ was well on its’ way to a rusty death when he sold it to be a trail rig.
 
4.0s are known for shedding iron. I wouldn't jump to piston skirt issues right out of the gate unless it has a noticeable knock. These engines have iron everywhere and the timing chains are also known to loosen a bit over time which is harmless but would increase iron. What is your oil pressure at hot idle? Does it run hot?

I replaced the cylinder head preventatively on my 2000 XJ 4.0L at 84k miles with a head from Alabama cylinder. Sold it with 200k no issues. Mine liked oil with moly in it, you might want to try something like Valvoline Maxlife synthetic 10w30, or a HDEO like a 15w40 or 5w40 as others suggested just to see if there is any change. I'm not sure how much moly the current blend of PYB has. I have a UOA floating around here somewhere with PYB 10w30 and had 9ppm iron from my 2000, but that was when PYB had a fairly healthy dose of moly.
 
Less than 20,000 miles since 2014? You've probably got significant corrosion in there from it sitting. Drive it more, it'll likely track down.
Maybe not "this" ....

Theory 1: not driving enough caused this wear issue
Theory 2: head swap caused this wear issue
Theory 3: something other than T1 or T2 caused the wear issue


Facts we can take from the limited info given:
- From 2000 (new) to 2014, they drove about 100k total miles; averaged 7k miles per year over 14 years. The wear in 2014 was perfectly fine all the way around. We'll presume the wear was good for whole 14 years.
- Then from 2014 to 2021, the driving went down a bit to around 4k miles a year. But wear went WAY up somewher in that time frame.
- Driving distance is around 3.5k miles annually over the last 6 months (1.75k miles over roughly 6 months). Wear has stayed "up" over the last 6 months.

So the major wear-rate change happend somewhere after 2014 and before 2021. That aligns with the major mechanical work, but I find it hard to believe that changing a head caused a cylinder/piston issue. There's not enough Si to blame it on dirt intrusion from the work done, nor an intake tract leak either.

I also find it hard to believe that going from 7k miles a year (a fairly low use rate), to 4k miles a year (even lower use rate), suddenly caused a HUGE spike in piston/cylinder wear. That is a massive spike in wear to blame solely on a slightly-lower use of the vehicle. Think about the "you're not driving it enough" logic suggested in the above posts ... So the owner drives it 40% less, but sees wear jump up 17x higher??????? Nope - I don't buy the "drive it more and it will be fine" logic; that's absurd.

With two UOAs being 7 years apart, it's just too hard to know "when" this wear issue really occured. Did the wear-rate change happen before or after the head work? None of us know for sure.


I think what we're looking at is "coincidence". I believe there's a piston/ring/cylinder issue that just happened to occur somewhere in that same 7 year interval where both driving distance dropped and head work was done. However, because there's not a good history of the wear-rates (7 years between UOAs), we can't say "when" it happend with any accuracy. Just because there is correlation between the head work and the wear-rate change, does not automatically mean the head work caused the wear issue(s). The two events coincide, but that does not mean one caused the other. Same goes for driving less; that happened somewhere in the same 7 year time-frame, but driving less should not cause wear to go obscenely high.


Theory 1 fails to make sense ... driving 40% less should not cause wear to shoot-the-moon by going SEVENTEEN TIMES higher.
Theory 2 fails to make sense ... there's no logic to saying a head-swap should result in massive piston/cylinder wear.
Theory 3 makes the most sense; something other than T1 or T2 caused the wear to spike during that time from 2014 to 2021.


One should never confuse correlation with causation; I've said that repeatedly over the years here at BITOG. But, one should also not confuse correlation with coincidence; just because two or more things occur at the same time, does not mean one caused the other.


My opinion ... I'd investigate the issue of a cracked piston, or whatever else these 4.0L engines may be known for in the piston/cylinder area.
 
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Thank you all for your responses. I had a 2am epiphany that I think explains the UOA results.

Years back I swapped out the stock air intake with a cold air intake style tube and cone filter. When I was cleaning the engine bay a few weeks ago I noticed the air filter had a chunk sliced out of it. Most of the slice didn’t go all the way through, but a small part did. Maybe a half inch by quarter inch? I threw the filter out and replaced it. I did look inside the throttle body and there was no dirt / dust build up so I thought nothing of this.

Looking back on it, I am now thinking that the wear on the UOA stems from possibly sucking up some tiny part of the filter. As far as how the heck that happened, I am not totally clear. The hose that connects the cone filter to the throttle body had the tendency to work itself loose because of the lever arm of supporting the filter and bumpiness of how the Jeep rides. I would simply tighten the hose clamp periodically. I want to say last fall I found it basically hanging off. Maybe the air filter contacted the fan belt? I need to look at engine bay to see what it might have hit, but definitely something that was moving quickly given how the damaged filter looked. Don’t think anything from outside could have done it. I have since fixed by adding a support below the filter tube and obviously changed the filter.

So now I need to think about what to do next. How plausible is it that there's still bits of filter in a cylinder? Seems the options are:
1) Do nothing, figure the UOA results might be residual filter debris
2) Something non-invasive like inspecting cylinders with boroscope
3) Remove head and inspect valves and cylinders, make sure there's nothing still in there.

Thoughts? Massively appreciate the help!
 
Maybe not "this" ....

Theory 1: not driving enough caused this wear issue
Theory 2: head swap caused this wear issue
Have you ever done a UOA on an engine that sat? I have. Unfortunately I can't find it at the moment, but iron was over 134ppm. It was, conveniently, also a vehicle I did a head swap on, in the fall, and had some other mods I was doing to it, so I wasn't driving it (it was my old Lincoln) and so it sat. It sat for quite a while. It got moved in and out of the garage a few times after the swap, then again 8 months later when the summer came around and I did more work on it which of course didn't help with start-up enrichment taking place and then it sitting more. Finally got it together and put a few thousand km on it then did a sample. It looked very much like the OP's. After I started driving it regularly, things went back to normal.

I'm not suggesting that the iron is coming from the car being driven less, I'm suggesting it's coming from corrosion forming in the bores when the vehicle sits for an extended period of time. This is why we typically "fog" marine engines in the fall, to avoid bore corrosion over the winter, though there's some question as to the actual need for that with engines operated in fresh water as long as they are shut off hot and not restarted. Startup enrichment (fuel) will negatively impact the oil film left in the bores and the moisture from that same phase of operation introduced during those quick start and move sequences aides in facilitating the corrosion.

Now, I'm in a much cooler climate than the OP, so I suspect the opportunity for the same situation to play-out in Socal is less likely. However, if they are doing quick start ups, moving the vehicle a short distance and shutting it off then letting it sit for an extended period, the opportunity still exists.

I think we'd need more details on the vehicle's operating profile to confirm whether this is a possibility it not, but I figured I'd throw it out there because I've experienced it.
 
Thank you all for your responses. I had a 2am epiphany that I think explains the UOA results.

Years back I swapped out the stock air intake with a cold air intake style tube and cone filter. When I was cleaning the engine bay a few weeks ago I noticed the air filter had a chunk sliced out of it. Most of the slice didn’t go all the way through, but a small part did. Maybe a half inch by quarter inch? I threw the filter out and replaced it. I did look inside the throttle body and there was no dirt / dust build up so I thought nothing of this.

Looking back on it, I am now thinking that the wear on the UOA stems from possibly sucking up some tiny part of the filter. As far as how the heck that happened, I am not totally clear. The hose that connects the cone filter to the throttle body had the tendency to work itself loose because of the lever arm of supporting the filter and bumpiness of how the Jeep rides. I would simply tighten the hose clamp periodically. I want to say last fall I found it basically hanging off. Maybe the air filter contacted the fan belt? I need to look at engine bay to see what it might have hit, but definitely something that was moving quickly given how the damaged filter looked. Don’t think anything from outside could have done it. I have since fixed by adding a support below the filter tube and obviously changed the filter.

So now I need to think about what to do next. How plausible is it that there's still bits of filter in a cylinder? Seems the options are:
1) Do nothing, figure the UOA results might be residual filter debris
2) Something non-invasive like inspecting cylinders with boroscope
3) Remove head and inspect valves and cylinders, make sure there's nothing still in there.

Thoughts? Massively appreciate the help!
Do you still have the stock air intake? If so, I'd start with putting that back on. The only thing the aftermarket setup is going to give you is the headache you are currently experiencing with it.
 
I think it's more than dirty air for awhile.

I would pull the oil pan.

My 4.0 developed a ticking sound that was most likely a cracked piston skirt.

Then sometime latter a chunk of piston skirt large enough to cause trouble broke off and jammed things causing catastrophic engine failure. Put in a reman engine.

Catch it early and you will need to put money into the engine to replace the pistons at least but save you the cost of an engine replacement.
 
Have you ever done a UOA on an engine that sat? I have. Unfortunately I can't find it at the moment, but iron was over 134ppm. It was, conveniently, also a vehicle I did a head swap on, in the fall, and had some other mods I was doing to it, so I wasn't driving it (it was my old Lincoln) and so it sat. It sat for quite a while. It got moved in and out of the garage a few times after the swap, then again 8 months later when the summer came around and I did more work on it which of course didn't help with start-up enrichment taking place and then it sitting more. Finally got it together and put a few thousand km on it then did a sample. It looked very much like the OP's. After I started driving it regularly, things went back to normal.

I'm not suggesting that the iron is coming from the car being driven less, I'm suggesting it's coming from corrosion forming in the bores when the vehicle sits for an extended period of time. This is why we typically "fog" marine engines in the fall, to avoid bore corrosion over the winter, though there's some question as to the actual need for that with engines operated in fresh water as long as they are shut off hot and not restarted. Startup enrichment (fuel) will negatively impact the oil film left in the bores and the moisture from that same phase of operation introduced during those quick start and move sequences aides in facilitating the corrosion.

Now, I'm in a much cooler climate than the OP, so I suspect the opportunity for the same situation to play-out in Socal is less likely. However, if they are doing quick start ups, moving the vehicle a short distance and shutting it off then letting it sit for an extended period, the opportunity still exists.

I think we'd need more details on the vehicle's operating profile to confirm whether this is a possibility it not, but I figured I'd throw it out there because I've experienced it.
Yeah - I've seen plenty of UOAs on vehicles which sit for long periods.

If that's the core issue here, what's the solution? Some people would say "drive it more often" ... but we also know that short trips are not always condusive to solving wear issues. Others would say "don't drive it as much, but drive it for longer operational cycles". OK - that makes sense. But ... the vehicle will be generally for the times it's needed. Does it make sense to jump in a car just to "drive" the wear rates down (at the expense of gas today??? OUCH!). Makes little sense to fog the engine; probably would kill the MAF sensor in the attempt?

Again - it was doing fine averaging 7k miles a year; evidence in the initial UOA. Now it's 4k miles a year, and it's gone sky-high in Fe, Cr and Al. I don't believe it's anything but piston/cyl wear (not a cam, or there'd be more Cu and no Cr to speak of).

Could it be the low annual mileage? Yes; I agree with you that it's possible. I also agree there's not really enough data preceeding the wear escalation; a 7 year gap is a long time to allow for guesses.

When the head was off, did the OP turn the crank over and look at the bores? That would have been an excellent time to notice any potential wear in the cylinders! Maybe it's time to invest in a bore scope and peer down there??? Probably the cheapest way find out what's really going on.

But, the "wear" is they symptom. What's the root cause? Whether it's sitting for too long or not, I don't think the condition is desirable by any means, so we need to step towards a resolution. IOW, what's the "cure"? Drive it a lot and see if it goes away? If that doesn't fix the issue, then it's pretty much drive it until it shatters a piston or galls a cyl wall?

He said it's been "babied", so we can only presume it's in good shape otherwise and probably worth keeping. So maybe a reman'd engine would be the final step?
 
Yeah - I've seen plenty of UOAs on vehicles which sit for long periods.

If that's the core issue here, what's the solution? Some people would say "drive it more often" ... but we also know that short trips are not always condusive to solving wear issues. Others would say "don't drive it as much, but drive it for longer operational cycles". OK - that makes sense. But ... the vehicle will be generally for the times it's needed. Does it make sense to jump in a car just to "drive" the wear rates down (at the expense of gas today??? OUCH!). Makes little sense to fog the engine; probably would kill the MAF sensor in the attempt?

Again - it was doing fine averaging 7k miles a year; evidence in the initial UOA. Now it's 4k miles a year, and it's gone sky-high in Fe, Cr and Al. I don't believe it's anything but piston/cyl wear (not a cam, or there'd be more Cu and no Cr to speak of).

Could it be the low annual mileage? Yes; I agree with you that it's possible. I also agree there's not really enough data preceeding the wear escalation; a 7 year gap is a long time to allow for guesses.

When the head was off, did the OP turn the crank over and look at the bores? That would have been an excellent time to notice any potential wear in the cylinders! Maybe it's time to invest in a bore scope and peer down there??? Probably the cheapest way find out what's really going on.

But, the "wear" is they symptom. What's the root cause? Whether it's sitting for too long or not, I don't think the condition is desirable by any means, so we need to step towards a resolution. IOW, what's the "cure"? Drive it a lot and see if it goes away? If that doesn't fix the issue, then it's pretty much drive it until it shatters a piston or galls a cyl wall?

He said it's been "babied", so we can only presume it's in good shape otherwise and probably worth keeping. So maybe a reman'd engine would be the final step?

I think a good first step would be a filter dissection to see if there's any metal caught in the filter. If it's something significant, the odds are, we'll see some metal particulate in there. If it's just corrosion, we shouldn't.

I also think he should fix the air intake tract, since it sounds like it's pretty heavily jerry rigged, and re-fit the factory intake if he's still got it.

I think some decent driving with a few short changes then do a sample after 5,000 miles to get a sample of the current wear rate after some decent use would do to establish a baseline. If things are still highly elevated, it's likely time to look a bit deeper. If they've dropped back down to levels that approach normal, then at least we know the condition was transient and have an idea of what the cause may have been.
 
I totally baby this Jeep (been in family since new and I'll have it forever) and keep up with all maintenance items. I replaced the cylinder head back in 2015 (30,000 miles ago). Prior to the head swap, which I did preventatively because the 4.0s in this year had heads prone to cracking, UOAs were flawless. These two UOAs were the first I've done since (kicking myself). No clue if the head has anything to do with it; it's been 7 years since the swap, but that's the only major work that's ever been done to the engine.

What's the best way to start troubleshooting other than ripping it apart? Compression test? No symptoms whatsoever, runs like a top. Unchanged oil pressure, no oil consumption, no weird noises. If it wasn't for the two bad UOAs I would say it's running perfect.
It's clearly related to the head swap. Still got the original head?
 
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