~150K Mile Jeep 4.0 - Engine Internal Pics

[SwampSurvivor]

Grabbed these the other day. Not the best quality (oil dripped on the phone taking a picture).

Engine has around 150K miles on it I believe. Legally, the vehicle has 201K on it.

I tried to get a picture of the bottom of the piston and the piston wall for one of the cylinders - unfortunately oil dripped on the phone and the picture came out blurry. But there is no scoring on the walls that I could see and , apart from some varnish ... doesn't appear to be any crud on the cylinders. So I believe the engine has never been severely overheated.

The milky stuff in the pan kind of worries me - the other stuff is dirt that fell into the oil pan on the way out. Not sure what to think of the milky stuff; it has not milkshaked the oil cap yet so I believe it may just be residual moisture from it taking a swim last fall. Or just from it raining a lot lately.

I got it at 95K miles and it has had a bunch of various oils - never run more than 6000 miles.

I will probably get valve cover pictures soon. That is leaking also.

 

[gomes512]

Looks like my old 4.0 when I had the pan off, had the same varnish color everywhere at 185K. No problems to report, it never really consumed oil at a appreciable rate either.

It's been a long time since I dropped a pan on one of these but is that a baffle on the top of the picture where the milky stuff is coming from? Is it possible that there is moisture trapped under there or that the pan has pin holes from corrosion that you can't see? I remember my '94 Grand Cherokee developing pinholes in the oil pan.

 

[Donald]

Any chunks of metal in the oil pan? Some years of that engine have a habit of cracking the piston skirt, latter a chunk of the piston skirt falls, sometimes into the oil pan and life goes on. At least for awhile. Other times the chunk jams the crankshaft/rod and catastrophic engine failure occurs.

 

[440Magnum]

You gonna slap a HV oil pump in there while the pan's off? Good insurance as clearances start to open up. These are a little like a smallblock Chevy in that the oil pump is sized so that there's not a huge amount of surplus flow and the pressure relief valve doesn't spend much time open, which also means that as the engine (and mainly the oil pump itself) wears a bit they become oil-pump limited. BTDT with my 2001, but a new oil pump put all back right and its soldiering on with its new owner, criss-crossing Texas regularly.

I seriously would NOT worry about piston skirts, that "weakness" is ridiculously exaggerated. A shop owner who works on hundreds of these per year said "they supposedly do WHAT?" and then laughed when I mentioned the internet flurry over it a couple of years ago.

 

[SwampSurvivor]

Originally Posted By: Donald
Any chunks of metal in the oil pan? Some years of that engine have a habit of cracking the piston skirt, latter a chunk of the piston skirt falls, sometimes into the oil pan and life goes on. At least for awhile. Other times the chunk jams the crankshaft/rod and catastrophic engine failure occurs.


Surprisingly enough, no. This engine sounds pretty bad for knocking but as I discovered, my flexplate is cracked. Hopefully it solves the issue.

Originally Posted By: gomes512
Looks like my old 4.0 when I had the pan off, had the same varnish color everywhere at 185K. No problems to report, it never really consumed oil at a appreciable rate either.

It's been a long time since I dropped a pan on one of these but is that a baffle on the top of the picture where the milky stuff is coming from? Is it possible that there is moisture trapped under there or that the pan has pin holes from corrosion that you can't see? I remember my '94 Grand Cherokee developing pinholes in the oil pan.


There is a baffle where it came from. The Jeep went for a swim in October and there was a lot of rain and dampness lately. Also - whoever opened this engine up before forgot to tighten the oil pan bolts in the back (they were literally backed out) so my guess is some moisture can work it's way in through that.

Originally Posted By: 440Magnum
You gonna slap a HV oil pump in there while the pan's off? Good insurance as clearances start to open up. These are a little like a smallblock Chevy in that the oil pump is sized so that there's not a huge amount of surplus flow and the pressure relief valve doesn't spend much time open, which also means that as the engine (and mainly the oil pump itself) wears a bit they become oil-pump limited. BTDT with my 2001, but a new oil pump put all back right and its soldiering on with its new owner, criss-crossing Texas regularly.

I seriously would NOT worry about piston skirts, that "weakness" is ridiculously exaggerated. A shop owner who works on hundreds of these per year said "they supposedly do WHAT?" and then laughed when I mentioned the internet flurry over it a couple of years ago.


I was planning on putting a high volume oil pump in. But the flex plate deal is a bit more than I was expecting to spend right now. It's not my daily driver and with the money I have dropped on it so far this year (front locker, seals, spicer u joints, timken wheel bearings, control arms, "frame" stiffeners) I will let the oil pump slide for a bit. If I get a place with a garage in the next year or two I would like to go through and freshen up a few things - new head, new cam chain, hv oil pump.

I know a few personally that have broken pistons. It does worry me a bit. But since I'm (hoping) it's the flex plate knocking, I think I'm good. Also - a few weeks ago I ran this on a motocross track and it spent a good 9 or 10 minutes at or above 4000RPM each time along with hitting the rev limiter multiple times. I think if it was going to scatter a piston or two, that would have been it

The cam chain has a bit of slack. With stunts like that I'm most worried about tossing the chain or jumping a tooth or two.

 

[440Magnum]

They're not notorious for jumping time, but I hear you. I think a new timing chain and a new clutch are the minimums I'm going to do to the '99 before my daughter moves off to grad school with it. Its sitting at ~170k right now.

RE motocross track and hitting the rev limiter... yeah, the 4.0 does NOT like that kind of treatment even a little bit! I think its a combination of the relatively low SBC-like oil volume being pumped and the long crank and a block that has a little more flex than, eg., the slant-6 does.

 

[yvon_la]

inline 6 last forever, you could retrofit some kind of under piston oil skirter so it cool piston ( like big rig) aisde from that? looks good to go for a while

 

[SwampSurvivor]

I don't think I'll be doing the high RPM stuff too much more; it was just a one and one type of fun. I would like to go on the motocross track again, but will use 4WD (it's on the side of a hill) so I don't blow anything up! I will be putting synthetic back in, it should hold up to abuse that I'll be giving it.

Provided I get the flex plate changed in time, there is about 500 miles of towing that will be accompanying off road trips.

I have changed a timing chain on a 4.0. Not sure I want to do this one just yet. I'll try to keep it attached for now.

 

[Donald]

Originally Posted By: 440Magnum
You gonna slap a HV oil pump in there while the pan's off? Good insurance as clearances start to open up. These are a little like a smallblock Chevy in that the oil pump is sized so that there's not a huge amount of surplus flow and the pressure relief valve doesn't spend much time open, which also means that as the engine (and mainly the oil pump itself) wears a bit they become oil-pump limited. BTDT with my 2001, but a new oil pump put all back right and its soldiering on with its new owner, criss-crossing Texas regularly.

I seriously would NOT worry about piston skirts, that "weakness" is ridiculously exaggerated. A shop owner who works on hundreds of these per year said "they supposedly do WHAT?" and then laughed when I mentioned the internet flurry over it a couple of years ago.


And I guess the #331 heads never crack or the substandard Teves front calipers were not [censored]?

 

[440Magnum]

Originally Posted By: Donald
Originally Posted By: 440Magnum

I seriously would NOT worry about piston skirts, that "weakness" is ridiculously exaggerated. A shop owner who works on hundreds of these per year said "they supposedly do WHAT?" and then laughed when I mentioned the internet flurry over it a couple of years ago.


And I guess the #331 heads never crack or the substandard Teves front calipers were not [censored]?


Never said that 331 heads never crack, that is a much more common problem than pistons cracking (and I didn't say that "never" happens either, just that its a case of the internet blowing things out of proportion).

 

[SwampSurvivor]

I find it surprising when I see people throwing multiple head gaskets at "older" 4.0s just to find out they have a cracked head or warped head.

That's a big ol' chunk of cast iron. If you overheat it, repeatedly, it's going to warp or crack.

 

[440Magnum]

Originally Posted By: Miller88
I find it surprising when I see people throwing multiple head gaskets at "older" 4.0s just to find out they have a cracked head or warped head.

That's a big ol' chunk of cast iron. If you overheat it, repeatedly, it's going to warp or crack.


But not nearly as much (or as likely) as a big old chunk of aluminum given the same treatment!

However, any time a head gasket blows for any reason, the head should be checked for warping or other damage even if its an iron head. Gaskets don't usually blow spontaneously (except on old Chevy 400 v8s). Iron heads are far stronger than aluminum, but not immune to abuse.

 

[SwampSurvivor]

My friend's $300 CL neon has pretty bad piston slap from a severe overheat that really warped the head heated the pistons up a lot.