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Discussion Starter · #1 ·
Hey everyone,

Hoping to get some input on this issue. When I start my Jeep after it has sat for a while, it will make sort of a knocking/rattling noise after about 30 seconds of running (wish I could upload the audio/video of it somehow). This continues until I drive about 1 mile, then it goes completely away. It does it every time I do a cold start. It almost sounds like its coming from the fan area but it's hard to tell. I haven't noticed any loss in performance and the noise does not get louder when I'm driving.

When it was in the shop today (for something else), I mentioned this issue and they said they noticed it a little too but did not diagnose it. When I mentioned the fan, they didn't think that was the case and said it is "probably" some slight internal damage to the engine that has happened over time. They said that it's not ready for a rebuild and to keep driving it and as long as I change the oil regularly it could still last a very long time.

Would an engine issue go completely away after driving it for a mile? Could it be the fan (or something similar)? Are they blowing smoke up my a**? Obviously I need to have it diagnosed further, but any ideas? it's been doing this since I bought the Jeep 4 months ago.

Thanks in advance everyone! Appreciate it.
 

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Not sure w/o hearing it but assuming you have the 4.0 they're known for having a knock like a bad lifter. My 2000 does it. But like I said w/o hearing it, it could many things.
 

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Mine makes a similar noise on occasion especially when I back into my sloped driveway with the rear end sitting lower than the front... the engine will make a loud racket upon cranking the next morning. I quit parking that way and put some Marvel Mystery Oil in the gas tank and I haven't heard the noise lately.
 

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Discussion Starter · #4 ·
Not sure w/o hearing it but assuming you have the 4.0 they're known for having a knock like a bad lifter. My 2000 does it. But like I said w/o hearing it, it could many things.
I do have a 4.0. Don't lifters "tick" more than knock?

Would an engine issue go away after driving it a mile? I'm by no means a mechanic, but I would think it would be constant, no?
 

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Discussion Starter · #6 ·
Yeah I've been searching around this forum and bad lifters seem to match my problem. Anyone know how much it would cost approx. to fix? Or should I just continue to drive it for now until it gives me problems?
 

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Discussion Starter · #7 ·

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Mine sounds just like that but it's louder. It got even louder when I changed the oil, so I put a thicker synthetic in her not and she only sounds like a diesel until she's warm.... Just keep an eye on your oil level, And drive her normal. These 4.0's will last forever and take a bunch of abuse.... I once ran with 1-2 quarts of oil in my old xj for about 50-60 miles to get home.... Had no problems out of it. When I sold it it had about 350k on that motor and trans and still ran like a top
 

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Discussion Starter · #9 ·
Mine sounds just like that but it's louder. It got even louder when I changed the oil, so I put a thicker synthetic in her not and she only sounds like a diesel until she's warm.... Just keep an eye on your oil level, And drive her normal. These 4.0's will last forever and take a bunch of abuse.... I once ran with 1-2 quarts of oil in my old xj for about 50-60 miles to get home.... Had no problems out of it. When I sold it it had about 350k on that motor and trans and still ran like a top
Thanks bulldog. So you don't think I'll do any damage as long as I keep up with the maintenance?
 

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Discussion Starter · #11 ·
An brother you should be gravey! Just run a heavier oil in the warmer months and recommended in winter
Ok cool. Was about to take it back to the shop and tell them just to fix the damn thing before anything else got damaged.

I'm also going to run some seafoam through it before the next oil change just for good measure (thanks for the recommendation pi55edoff).
 

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It could be as simple as a manifold gasket, cracked manifold, or an issue where the exhaust manifold connects the exhaust pipe. Either will make a racket until it heats up and reseals. Had a similar problem where the pipe connects, pulled it apart cleaned it up, slopped it up with anti-seize, installed new bolts and tightened the snot out of it. No noise.
 

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Discussion Starter · #13 ·
Good point. It's odd because it's seems louder towards the bottom of the engine.

I've also been adding Rislone to each oil change.
 

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It could be as simple as a manifold gasket, cracked manifold, or an issue where the exhaust manifold connects the exhaust pipe. Either will make a racket until it heats up and reseals. Had a similar problem where the pipe connects, pulled it apart cleaned it up, slopped it up with anti-seize, installed new bolts and tightened the snot out of it. No noise.
Interesting. I do need a new exhaust.
Mine sounds exactly like that one.
I will try to tighten the manifold fasteners.

I was also told not to worry about the noise, and that these engines are bullet proof! :bottom: <---- HA
 

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Discussion Starter · #15 ·
Now I did have the exhaust from the 2 precats back replaced not too long ago. Should they have caught a manifold issue at that time?
 

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Discussion Starter · #16 ·
Just had it looked at by another shop. They used a stethoscope and said it sounds like a damaged lifter in the #4 cylinder. They're going to see if they can get a scope it to see if there is also camshaft damage, but sounds like at the minimum, I'm going to need to replace the lifters/followers. This sucks!
 

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I've got a 2000 with the 4.0. It had the lifter noise when I purchased it. I drove it awhile and when I changed oil, I added a quart of Marvel Mystery oil to it. After a couple hundred miles the noise was gone. I've since put about 5000 miles and another oil change again using Marvel Mystery oil and still do not have any lifter noise anymore. It was a cheap fix and worked in my situation. Just food for thought.
 

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The problem is lifter and cam shaft. I just got done talking to a machine shop here and they rebuild 4.0 and stroke them for my area.

The guy said that every 4.0 that they have rebuilt in the last 20 years 100% have been because of camshaft failures.

The 4.0 and most of the race engines have flat tappet cams instead of the newer roller cams. The problem started back in 2007 when the government regulated the additives in the oil and removed the Zinc and phosphorus (ZDDP) out of the oil. This was not a problem for roller cams, but a big problem for flat tappet cams. The reason they did this was because the ZDDP was causing premature cat converter failures around the 50 - 80 k range. ZDDP is an additive that adds additional lubrication that the flat tappet cams need. But, this also caused cam failures in the 4.0 at circa 150K. The noise you hear is the flat cam lobes slapping against the lifters. After a while the extra hardness coating on the cam lobe wears off and begins to damage the lifter and the space between the cam lobe and the lifter increases. Or the lifter begins to cup.

He did not suggest changing the lifters without changing the cam.

If I couldn't do the above he did suggested that I buy a case of cheap oil filters and replace them every 1k. Not the oil just the filter. The reason is that as the cam begins to wear the lifter is also wearing itself and little particals of metal begin to fall off. Eventually the oil filter plugs and begins to bypass. As the particals increase they get into and around the bearings. The crank is hard metal whereas the bearings are soft. When the bearing channels fill up with the hard metal particals from the cam and lifters you then have hard metal bearings on hard crank metal........a perfect place for failure.

If you have a 4.0 You should be adding Risoline Zinc additive or be using Joe Gibbs racing oil which has the zinc additive.
 

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Discussion Starter · #19 ·
I've got a 2000 with the 4.0. It had the lifter noise when I purchased it. I drove it awhile and when I changed oil, I added a quart of Marvel Mystery oil to it. After a couple hundred miles the noise was gone. I've since put about 5000 miles and another oil change again using Marvel Mystery oil and still do not have any lifter noise anymore. It was a cheap fix and worked in my situation. Just food for thought.
I thought about trying some of that, which I still may. What I'm concerned about is, if it's truly a damaged lifter, additives are only going to mask my issue. there's also the question of what caused my lifter issue. I certainly don't want to replace it only to have the new one damaged. I Gould know more by Tuesdy
 

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I thought about trying some of that, which I still may. What I'm concerned about is, if it's truly a damaged lifter, additives are only going to mask my issue. there's also the question of what caused my lifter issue. I certainly don't want to replace it only to have the new one damaged. I Gould know more by Tuesdy
read my first post!!!!!!! Unless your mechanics know about flat tappet cams they won't know what caused it. Check with the machine shops in your area that rebuild 4.0's, they will know.
 
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