Notorious Knock -
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post #1 of 7 Old 03-21-2016, 07:48 PM Thread Starter
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1995 ZJ 
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Notorious Knock

Hey guys. I'm having a bit of trouble with my 4.0L in my 95 ZJ. I recently bought the engine back in November and I've never noticed a knock on the engine until now(started to recently make the noise, couldn't tell from November to end of December, had no muffler.) Its a faint knocking noise which sounds like it's coming from the bottom of the oil pan. I'm thinking bearings but my oil pressure doesn't fall under 20 psi, the lowest I seen it was a little below 30 psi (pressure fluctuates with acceleration.) The noise is in sync with my rpms and it quiets down sometimes. I also thought it was a lifter, since I've been using 5w-20. Just put 10w-30 in it last week along with valve medic, still no luck. What could it be? A family mechanic said its nothing I should worry about, and just drive it till it dies but I really would like to avoid buying and installing another engine. Thoughts? Any help is appreciated. Thanks.

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post #2 of 7 Old 03-21-2016, 10:07 PM
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1998 ZJ 
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Why on earth did you use 5w20? It may have damaged your engine.
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post #3 of 7 Old 03-22-2016, 09:14 AM
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1996 ZJ 
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Lower half knocking noise with consistent oil pressure; sounds like you spun a bearing. A loss of oil pressure and you would have wiped a bearing.
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post #4 of 7 Old 03-22-2016, 10:50 AM
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1996 ZJ 
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Originally Posted by StPaul59 View Post
Why on earth did you use 5w20? It may have damaged your engine.
This. 5w20 is way too thin for these old tractor engines. My 08 caliber calls for 5w20 and when you pour it in it's noticeably thinner than any other oil I've ever used.

You could try dropping the pan and changing the lower bearings to quite the noise but that will just buy you some time until you rebuild or replace the engine.

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post #5 of 7 Old 03-22-2016, 01:04 PM Thread Starter
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1995 ZJ 
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Sorry, meant to say 5w-30, but I put that in my engine because that's what the 95 calls for?
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post #6 of 7 Old 03-22-2016, 01:18 PM
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You're fine using 5w-30.

My 94 also has a very faint knock but I believe its lifters. Its done it for 3 years now and hasn't changed (Over 30,000miles) so I'm not worried about it. The lifters seem to be getting progressively worse though. For a good year they stopped ticking all together but now they normally tick to some extent till the oil warms up. Sometimes its very very loud. Like you can hardly talk standing beside of the Jeep loud.

1994 ZJ-I6 w/216,000 mi
1998 ZJ 5.9 w/65,155 mi Slate Black
2004 KJ w/90,300 mi
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post #7 of 7 Old 03-23-2016, 02:07 AM
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1998 ZJ 
Join Date: Aug 2010
Location: Virginia
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I havent yet seen a 4.0 that doesnt have some sort of knock or clanking noise at idle. AKA hense the name tractor engine lol.

Record a video and upload it on youtube or something so we can hear the noise.

Try putting a bottle ZDDP in the oil. I did that and it quieted up both of my engines big time. These engines like alot of zinc, and sadly thanks to Obama motor oil has mostly removed Zinc from our oil.
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