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Unread 06-05-2012, 11:14 AM   #1
DerMeister
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4.0L Lower end noise? Videos within

My 2000 xj developed this noise a couple years ago. It seems like a lower end knock that is sometimes hard to hear, but other times is very noticeable. It only does it when up to operating temp, and it sounds louder during the summer.

Mileage is 114,000
Oil is Rotella 15w-40(I used to use 10w-30 but am trying Rotella for the summer months)
Filter is Wix 51515

Oil pressure is great, 25 at idle, 50 at speed. No coolant loss, oil is clean and stays clean.




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Unread 06-05-2012, 01:06 PM   #2
Azzy
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Have you done a compression test?
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Unread 06-05-2012, 01:27 PM   #3
BassMasterCHS
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Does it stay the same under load and deceleration? I have a similar noise that I suspect is a main bearing knock.
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Unread 06-05-2012, 02:18 PM   #4
jeepkid03
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That is normal for the 4.0L. Almost every 4.0 I have heard has that slight idle knock. Some do it more than others, especially high mileage motors. Mine has done it since I bought it, my previous '90 made that noise, my dad's '87 made that noise, and my buddy's 2000 also makes the noise. I seem to only notice it in mine when I run a 10w40 oil. 10w30 seems to quiet it down a lot.

Try Pennzoil Yellow Bottle 10w30 and see how that does. It has lots of moly in it, and seems to quiet my 4.0 down.
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Unread 06-05-2012, 08:28 PM   #5
Oregon187
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Mine is an 01 and it makes the exact same noise. I am hoping that it is normal too, my brother has a ZJ with a 4.0 that also makes the same noise.
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Unread 06-05-2012, 09:20 PM   #6
DerMeister
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Quote:
Originally Posted by Azzy View Post
Have you done a compression test?
No, I will be doing a compression, or leak down test in the next few months when I change the plugs and boots.

It goes away under acceleration and it only existent at idle.

Glad to hear this is normal for the most part, does anyone know exactly what it is? I've been keeping an ear on it, but thankfully the noise has stayed the same.

It isn't torque converter bolts either.
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Unread 06-06-2012, 08:11 AM   #7
Oregon187
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Yeah, I checked my flex plate bolts and they were fine too.
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Unread 06-06-2012, 06:30 PM   #8
Oregon187
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Bump. Anyone else have an opinion on this issue? I'd really like to hear from some more of the experts around here that have owned 4.0's for many years.
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Unread 06-08-2012, 09:49 PM   #9
DerMeister
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Another bump, I am interested if anyone knows what it is for sure as well.
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Unread 06-08-2012, 10:01 PM   #10
1CVPaul
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So I'm the second owner of mine. PO was anal about keeping records ( bless his heart ). One of the items in the extensive file he had kept on the xj, was a copy of a letter to Chrysler he sent soon after he had purchased it regarding the " knocking at idle ". According to them it is normal. I had heard that it had something to do with a coating that the factory put on the pistons. Mine sounded like a diesel at idle until I rebuilt it. Now, with new pistons and re-bore, it sounds more like a sewing machine. Quite ! Bottom line - nothing to worry about. Typo "quiet"
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Last edited by 1CVPaul; 06-09-2012 at 02:56 PM.. Reason: typo
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Unread 06-09-2012, 02:26 AM   #11
IndridCold89
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Here's mine making that exact same noise. Threads about this help me worry less about it, lol.
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Unread 06-09-2012, 05:17 AM   #12
Pats94
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I'm makes the same noise, has for a long time, at least 90,000 miles. I chalked it up to piston slap.
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Unread 06-07-2013, 08:27 PM   #13
zachm
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My 2000xj just started making the same noise at 126k. It only happens at start up. The noise goes away after driving a short distance. I was starting to get worried about it, maybe this is just normal?
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