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Old 08-28-2012, 01:12 PM   #1
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4.0L engine knock on start up

hello experts,
i solved the rear spring clunk now i got a knock in my 2002 4.0L with 110000 miles on it, it seems to be only on startup, it tends to go away after about 5 minutes of driving, i dont believe it increases with rpms, or at least its inaudible due to the normal engine noise. its a 2002 with a build date of december 2001, so is the bad head still a option? i dont have any other signs of a blown head gasket like smoke, oil pressure issues ect...any thoughts will be greatly appreciated, thankyou guys

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Old 08-28-2012, 01:25 PM   #2
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My 2002 TJ has the same problem; I've talked to several friends and they say don't worry about it. I tried the Seafoam oil treatment and didn't help. My TJ has 165000 miles on it and I just bought it June; no oil leaks, no smoke. So far it hasn't caused any problems. I have a 2000 Cheorkee with the 4.0L with 197000 miles on it and it is fine. Would like to know if there is a breakdown in my near future; otherwise I will just ignore it like my friends said.

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Old 08-28-2012, 05:40 PM   #3
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Mine does same thing. 02X 4.0
Mostly in colder weather for the first couple minutes. Started a long time ago and have 182k now. Not a problem yet.

Just to be more specific now that I think about it... U talking knocks or taps??
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Old 08-28-2012, 05:49 PM   #4
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+3 Mine sounds like a diesel rattling/knocking until it is fully warmed up. It's an '02, 4.0 as well. My neighbor's '99 does it too and has for a long time. I noticed a little thinner motor oil helps it, but I don't want to run thinner than 10W-30.
Did the Seafoam in the oil for a while, too. No change.
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Old 08-28-2012, 06:23 PM   #5
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Also have an 02. Same thing. 135,000 miles. Seafoam has quieted it a little. Next up is changing out the headers as I'm pretty sure I have a crack.
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Old 08-28-2012, 06:38 PM   #6
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00 147,00 mile same thing sounds like crap, My super mechanic checked everything and told me to drive it till it breaks. he say's he see's them all the time like that on the 4.0. 12k miles and still running
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Old 08-28-2012, 09:27 PM   #7
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so i gather that this is common and no catastrophies yet? i repeated the process approx 4 times today, upon start up it has a knock if i drive 100 feet and stop at a light, i can not hear it anymore, no differences were heard when the engine was warm or cold....i just dont want to be starving my engine of its lube, checked oil level and all seemed well there as well....i just dont wanna do unwanted damage due to my ignorance, ....
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Old 08-29-2012, 08:29 AM   #8
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No catastrophies on mine yet.
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Old 08-29-2012, 10:47 AM   #9
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I've only put about 2k miles on mine; no "known" issues yet. Turn up the audio before you start the engine and everything will be fine:-)
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Old 08-29-2012, 11:29 AM   #10
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I just sorted out a weird knocking this morning. I got the truck last week, it was quiet. But for a few days now I was getting what sounded like a deep bearing knock whenever I put it in drive. It was constant, but never really changed pitch with RPMs. I checked under the hood, firewall and chassis for anything loose or touching. I was convinced it was a bearing.

Turns out it was the 4wd handle. I don't know whether it was a noisy linkage under the hump, or it wasn't fully disengauged. But I pushed it down hard and the noise stopped.

Probably not the OP's problem, but it's something simple to look at.
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Old 08-29-2012, 11:39 AM   #11
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Wow, my 02 X with the 4.0 110k miles does this also once in a while. Its been hotter than shit around N.M so not sure if it has anything to do with the weather.

First time it did it the Jeep was cold, I heard the knocking and listened to it for a sec before slighly bringing the rpms up. As soon as I did the sound went away.
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Old 08-29-2012, 11:50 AM   #12
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Mine goes away under engine load, too. Only idling when it knocks and rattles. Gone when warmed all the way up. I dunno...It can't be good having parts banging around rather than sliding quietly on a film of oil, but I can't afford to worry about it right now. Seems pretty common.
Kewrock, I am pretty sure it's in or on my engine, but I will look at the handle and attachments underneath.
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Old 09-28-2012, 05:41 PM   #13
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I know it's been sometime since this has been talked about but...

Finally got new headers on. Knocking / ticking when cold on start up seems to have disappeared. Could be that the old headers were cracked (originals with 130k miles) or maybe it was the rear main seal leak that was also fixed.

Either way it's gone and sounds new.
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Old 09-28-2012, 06:03 PM   #14
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Ticking is normal but a low-end knocking noise at startup and for the first five minutes is frankly pretty scary sounding to me. I'm thinking it may be bad rod bearings.
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Old 09-28-2012, 07:42 PM   #15
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So I had a friend listen to it and he's been a Master Mechanic for more than 20 years. Sounds like lifter rattle to him. I replaced a quart of oil with Marvel Mystery Oil and drove it for a couple weeks. It sounds somewhat better now, but I think it will still rattle cold until rebuild someday.
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Old 09-28-2012, 10:07 PM   #16
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Hydraulic lifters are a bitch. Just don't rev the engine until the oil pressure is built up.
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Old 09-29-2012, 12:59 PM   #17
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Hmmmmm. I have a 97 4.0 auto with 85K on it, and it is as quiet as anything. Been running Mobil 1, but I doubt that is why.....
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Old 09-29-2012, 01:34 PM   #18
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... Been running Mobil 1, but I doubt that is why.....
Right on it not being because of the Mobil-1 because I run nothing but conventional 10W-30 like from Valvoline or Castrol and mine with 90K miles is "quiet as anything" too. That also describes my previous TJ with nearly 200K miles on its 4.0L engine running nothing but coventional Valvoline/Castrol motor oil when it was stolen.
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Old 09-29-2012, 09:08 PM   #19
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I just run Quaker State Defy. I guess it's a blend, so probably 70% conventional. Otherwise I'll just run straight conventional and save a few bucks. No need for synthetic in this engine, but nothing wrong with it either if you want to...Pretty sure it doesn't have anything to do with the lifter rattle either way.
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Old 10-29-2012, 08:43 AM   #20
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I got my 1998 4.0 manual 5 speed sport, and it has the tick. It has been between 30 and 60 degrees outside, and it has the tick til it gets near running temp of 210 then quits. And what is the normal running temp?
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Old 10-29-2012, 10:55 AM   #21
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About 210 F for the coolant temp. gauge. Oil warms up a bit slower, and usually ends up running somewhat hotter than the coolant temperature after driving for a while--depending mostly on engine load.
I noticed mine doesn't tick right away. It starts after a minute or so, and then fades away about when the temperature guage is reaching 210 F. It may tick under load, but the engine noise drowns it out. It's not super loud, but definitely noticeable when it's idling.
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Old 12-26-2012, 07:30 PM   #22
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Question 2004 knocking

I just got a 2004 jeep tj not long ago. I really like it but its got a knocking sound i really dont know if its coming from the top of the motor or the bottom. The only thing i can really say about it is it has 80000 miles when i first got it it was fine no sounds ran and sounded great. Well i did my first oil change and at frist i put mobal 1 in it and i had a knocking sound when i first started it up. But to let you know it just so happen the temp had went from the 60s to the 30s in this time. Well i called a dealer and they told me that they would pull that oil out so i did and put conv, oil in it and it seemed to help. But now when it first start it in the morning its still cold it starts fine and then it will knock for a few mins pertty load just untill it warms up then goes away and sounds good. So what do yall thank would make one start and sound good for a min or so then start knockin untill it warms up to about 190 degress? So its a 4.0L and it has alot of power and dont use any oil. please help.
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Old 12-26-2012, 08:15 PM   #23
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So what do yall thank
Put some rotella 5-30 in there, and don't rev the motor until it's warmed up.
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Old 12-27-2012, 09:20 AM   #24
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Ok thanks for the info. What kind of oil filter would you use? Or could you tell me maybe what would mack it do that. Im just about to the point where i would try just about anything to keep my jeep running.
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Old 12-27-2012, 09:45 AM   #25
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Ok thanks for the info. What kind of oil filter would you use? Or could you tell me maybe what would mack it do that. Im just about to the point where i would try just about anything to keep my jeep running.
Hydrolic lifters lose their pressure when the engine sits. when it's cold it takes longer for them to build up pressure. when the pressure is down the spacing in the rockers, push rods, and lifters increases causing a knock. If you rev the motor you run a chance of bending a push rod, shoving a pushrod through the rocker.

Thin oil can reduce the time it takes for a lifter to build up pressure, but it also can take longer if the oil pump is weak.

If you really need to get moving in the morning, you could get a block heater installed in one of the freeze plugs, but that would require plugging it in at night.
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Old 12-27-2012, 09:58 AM   #26
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I own a 2002 4.0 with 120,000 miles and a tick developed in mine around 117,000. I did everything from seafoam, mmo, heavier grade oil and nothing stopped the tick. It eventually got louder and louder until something had to be done. first determine if it's top end or low end with a mechanics stethoscope. If it goes away after reaching running temp and sounds like top end it's more than likely a failed lifter or bent push rod. Take your valve cover off and check all the rocker arms to make sure none are loose also with the push rods. It might not be a bad ideas to start it up with the cover off the see if you have sufficient oil flow to the rocker arms. If its low end and the sound is not consistent with rpms it could be a cam bearing wearing out. I found out my problem after weeks of headache. For me my sound was consistent with the rpms and never went away when at nominal temp. 4 out of the 6 pistons had blown seals and some broken piston skirts. This is worst case scenario. Hope this helps some!
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Old 12-27-2012, 10:46 AM   #27
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4 out of the 6 pistons had blown seals and some broken piston skirts. This is worst case scenario. Hope this helps some!
What are these seals you speak of? Rings?
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Old 12-27-2012, 11:31 AM   #28
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Excuse me my mistake, yes rings xD
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Old 12-27-2012, 11:44 AM   #29
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I have the same problem with my 06 and 123000 miles. A friend of mine who works as an engine tech for a local dealer here told me, after checking it out, that it was piston slap. He said that the skirts are too short, to save money, and the piston slaps against the side walls until it warms up and gets a better seal.
I hope this helps because I was really worried myself about this problem until I talked to him.
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Old 12-27-2012, 12:43 PM   #30
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Thanks everyone for your input. I've had a few people tell me to go with thiner oil so ill try that and see what happens. Maybe ill have some luck with that. But all in all dang i like my jeep nothing says toy like a jeep does.

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