Catering oil choice to be piston skirt friendly?

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KCJeep

KCJeep

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Well after having my WJ Jeep for over a year, I've come to learn that the wonderful 4.0 in it had previously been tinkered with by Chrysler. It is not quite the same as the 4.0 I-6 I knew and loved in my previous two Jeeps. Anyway long story short Chrysler made a piston head change of some type in an attempt to improve emissions. Over the long haul these tweaked engines have exhibited a tendency to crack piston skirts and eventually disintegrate, usually resulting in a complete rebuild being required.

Mine runs like a top at 98k now. I obviously want to avoid this situation in the future (many of them run forever with no problem) and I'm wondering.... Is there any way to cater my oil choice toward babying the aluminum piston skirts? Someone suggested a thinner oil might be a better choice but I have no idea.

I have noticed in the year and a half I've owned it that my Jeep seems to prefer thinner oils, and it was never quieter than when I had PYB 5w30 in it. If it would be better for the skirts I'd be willing to run 5w30 in it all year round despite the 10w30 recommendation by Chrysler. Might even be willing to switch to QSUD for it if it could help.

Any suggestions/input appreciated.

Thanks!
 
Doesnt that engine have flat tappets ?? if so a high zinc or ZDDP content oil is definitely beneficial. My vote is for Rotella T6, M1 TDT 5w40 or QS Defy , in that order.

And if im wrong , sorry for wasting 3 seconds of your time ? lol
smile.gif
 
Originally Posted By: bourne
Doesnt that engine have flat tappets ?? if so a high zinc or ZDDP content oil is definitely beneficial. My vote is for Rotella T6, M1 TDT 5w40 or QS Defy , in that order


I agree. I'd be using good robust a 5w-X0 oil. Also, I privately wonder do the individuals that have trouble with historically durable engines do so because of a lack of maintenance, subpar choices in motor oil or just downright abuse the heck out of engine. Usually people aren't upfront with these sorts of contributing factors when they end up having problems.
 
I'm not entirely sure how any oil is going to stop damage to the piston skirts. Rings maybe - skirts? Doubt it.

This sounds like a problem caused by poor metallurgy or fabrication, or perhaps poor engine design causing one side of the skirt to slam against the cylinder. It's doubtful that any oil would help this.

If oil were the solution I'd think thicker would be better in this case.
 
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Those 4.0 seem to like a thicker oil from what I've seen. No real scientific evidence, but the ones I've heard run on xw-40 seem to be quieter. If I had one, I'd probably be running T6 in it.
 
Yes the 99-01's are best known for the issue but I've seen it pop up from time to time on Jeep forums to include 04's, although nowhere near as common.

Already using MMO in the gas (which it loves) and it is supposed to work as an upper cylinder lube, and MoS2 as well, so I guess I'll just keep on doing what I'm doing. I was curious if I could do anything with oil selection that would help.

While the common theme with the 4.0's is they "like thick oil" this doesn't seem to apply to the newest ones and mine will actually knock a bit if the HTHSV is too high. Purrs like a kitten on thinner stuff.

Thanks!
 
Chrysler switched to the aluminum pistons in 1996. All 4.0s 1996 and newer have the same pistons. '99-'01 had the head cracking issue, but besides that I wouldn't consider them "bad".

The piston skirt issue is spotty, there is NO definite year. I've seen them on '96s, '98s, a '99, and an '01.

I would just keep doing what you are doing maintenance-wise. As long as you keep up with the maintenance and don't spend most of your time around the rev limiter you should be fine.
thumbsup2.gif
 
Originally Posted By: jeepman3071
Chrysler switched to the aluminum pistons in 1996.


All 4.0L's used aluminum pistons. I have 6 from my kid's '89 freshly pulled.

In '96 they started using hypereutectic with coated skirts.
 
Originally Posted By: Zaedock
Originally Posted By: jeepman3071
Chrysler switched to the aluminum pistons in 1996.


All 4.0L's used aluminum pistons. I have 6 from my kid's '89 freshly pulled.

In '96 they started using hypereutectic with coated skirts.



You are correct, that is what I meant.
thumbsup2.gif


I also agree with mechtech2, piston skirt issues aren't really something you can help with a different oil selection. Just maintain the engine like you have been. Engine neglect will make the issue worse (such as overheating), but since you are on this forum I doubt your engine is neglected.
lol.gif
Far more 4.0Ls have cracked heads than piston issues, and even the cracked head isn't all that common. I know plenty of people with the crack prone casting who haven't had any issues yet with the original head.
 
Originally Posted By: jeepman3071
I also agree with mechtech2, piston skirt issues aren't really something you can help with a different oil selection. Just maintain the engine like you have been. Engine neglect will make the issue worse (such as overheating), but since you are on this forum I doubt your engine is neglected.
lol.gif



True that!

Well I just finished reviewing my stash of saved 4.0 UOA's. I can not find any significant difference between thick/thin or anything else as far as shedding aluminum goes. It does run nice and cool (it's in good shape and has the proper Chrysler HOAT in it) so I guess I'll keep doing as I am and run it to 200k as planned.

Thanks!
 
Originally Posted By: KCJeep
Yes the 99-01's are best known for the issue but I've seen it pop up from time to time on Jeep forums to include 04's, although nowhere near as common.

Already using MMO in the gas (which it loves) and it is supposed to work as an upper cylinder lube, and MoS2 as well, so I guess I'll just keep on doing what I'm doing. I was curious if I could do anything with oil selection that would help.

While the common theme with the 4.0's is they "like thick oil" this doesn't seem to apply to the newest ones and mine will actually knock a bit if the HTHSV is too high. Purrs like a kitten on thinner stuff.

Thanks!




If the PYB 5W-30 works for you...Use it.
 
Originally Posted By: lexus114
If the PYB 5W-30 works for you...Use it.


Sage advice right there, I've not found anything that seems to work as well even though I've spent a lot of time looking for another silver bullet (typical BITOG'er hah hah). Frankly I'm afraid of the 5w30 during the hot months, Chrysler spec'd 10w30 as the preferred lube for this engine I'm sure due to shear concerns and I have the same worries.

Anyway that's the reason for the heavier PYB blend I'm running now but even that is not as quiet as the 5w30 was. Maybe I'll try a short OCI and a UOA on the 5w30 to see how it goes.
 
Originally Posted By: KCJeep
Originally Posted By: lexus114
If the PYB 5W-30 works for you...Use it.


Sage advice right there, I've not found anything that seems to work as well even though I've spent a lot of time looking for another silver bullet (typical BITOG'er hah hah). Frankly I'm afraid of the 5w30 during the hot months, Chrysler spec'd 10w30 as the preferred lube for this engine I'm sure due to shear concerns and I have the same worries.

Anyway that's the reason for the heavier PYB blend I'm running now but even that is not as quiet as the 5w30 was. Maybe I'll try a short OCI and a UOA on the 5w30 to see how it goes.



Funny you say yours was quietest on the 5w30 PYB. That is the case with my 4.0 as well. I'm currently running 10w30 and it isn't as quiet as the 5w30. I ran 5w30 over the winter and my buddy who also owns a 4.0L said my jeep sounded quieter. I will probably go back to the 5w30 next change.
 
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