Need help identifying this engine noise

Joe.B

Joe.B

TJ Enthusiast
Joined
Sep 8, 2020
Messages
180
Location
Minneapolis, MN
I’m not sure what this sound is making my Jeep with the 4.0l 6cly sound almost like a diesel I’m not to good at engine stuff so I have no idea what it is. If you know anything or have an idea I would love to hear em
 
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Joe.B said:
It only happens on cold starts and goes away within 10 min of it running after it’s goes away completely
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Ok so we appear to be looking for an exhaust leak. Could be a cracked exhaust manifold, a failed manifold gasket or a compromised downpipe connection. The fact it subsides generally points to something expanding as it heats up to close the leak.
 
Like a rat a tat tat noise until it warns up?

That would be the infamous manifold gasket or manifold itself cracked.

No biggie. Start jeep...listen around that area. Put your hand near the noise under and over the manifold. You'll feel it if its6a bad leak. Feel the exhaust air. Don't touch the manifold as it gets hot...quick.

Good luck.
 
Ok so this is the first time that I’ve really payed attention to this noise but it’s been there sense I got it which was a few months ago I thought that it was just the engine warming up but the more I learn about Jeep’s the more I’m thinking that this is an issue. So when it’s warm and idling the sound goes away and it’s fine but if you rev it up and let it come back down the sound comes back for a few seconds then goes away when idling again I’ve been doing some research on it but I can’t find what it is I’m thinking it’s somthing to do with the valves because it sounds like it’s right there on the top end. I’m taking it in to the shop next week but I just would like some help from the great people on here to see if they can help my figure out what it might be
 
Next time, turn the engine off when it's hot and not making any noise. Wait a few minutes and restart. Does the noise return for a few seconds? If so, I'm guessing lifters. Not really a big deal IMO.
 
bromel said:
Next time, turn the engine off when it's hot and not making any noise. Wait a few minutes and restart. Does the noise return for a few seconds? If so, I'm guessing lifters. Not really a big deal IMO.
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I was thinking it was the lifters but I wasn’t sure
 
I’ve done some more lookin and I’m thinking it either a cracked piston skirt (hopefully not) or lifter ticking which I guess isn’t a huge deal
 
Joe.B said:
I’ve done some more lookin and I’m thinking it either a cracked piston skirt (hopefully not) or lifter ticking which I guess isn’t a huge deal
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A cracked piston skirt would sound consistent, not intermittent which is more indicative of a lifter. And it wouldn’t change much with engine temp.
 
bromel said:
A cracked piston skirt would sound consistent, not intermittent which is more indicative of a lifter. And it wouldn’t change much with engine temp.
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Oh ok good I’ve read that people say that the Jeep needs to be driven harder. I’m not sure if I should actually do that but maybe I drive like a grandpa I shift at about 2300 rpm so I’m not sure if I should rev it out more?
 
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Joe.B said:
Oh ok good I’ve read that people say that the Jeep needs to be driven harder. I’m not sure if I should actually do that but maybe I drive like a grandpa I shift at about 2300 rpm so I’m not sure if I should rev it out more?
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That argument is made to prevent carbon buildup and preignition. Some call it pinging. That’s not what you have, or at least that’s not what is causing this noise.
 
Joe.B said:
I’m not sure what this sound is making my Jeep with the 4.0l 6cly sound almost like a diesel I’m not to good at engine stuff so I have no idea what it is. If you know anything or have an idea I would love to hear em
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Sounds exactly like my '03 TJ. Morning after I bought it went out to start it and heard that noise. Had about 139k miles on it. Tried Seafoam, Different Oil Filter (NAPA GOLD/WIX), Heavier Oil, took oil pan off & looked at piston skirts, etc.....Didn't find any issues other than loose/worn timing chain. Based on the other's experience with replacing chain not correcting the noise, I decided to just drive it. Now has 152k miles on it and runs like a champ. Makes noise until it warms up. I say don't worry!
 
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Yeah I should also note that my TJ has had a similar noise since when I bought it at 75k. Now it has 108k and runs like a top. Quiet on startup, then you hear a little rattling after 15 seconds, then it goes away completely when hot. I've had an oil analysis done which came back saying I have a perfectly healthy engine.

Maybe a little Marvel Mystery Oil could help, but I don't bother.
 
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