Novak Conversions Jeep Wrangler TJ radiator

4.0 loud engine rattle until warmed up

dodgeboy

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I'm trying to diagnose a loud engine rattle on my 2005 4.0L 6-speed. Here are the characteristics:
  • It begins about 20 seconds after a cold start and quiets down significantly (but doesn't completely go away) after the engine is completely warmed up (10 mins or so, at 200F)
  • Sounds more substantial than lifter noise (I had lifter noise before and replaced the lifters to remedy it, so I'm familiar with the sound)
  • Even when cold, it does not make the noise when the engine is under load/accelerating.
  • It gets much louder at idle and when decelerating.
  • The noise does not change when the clutch pedal is pressed (it's not the throwout bearing, as I've also replaced that a couple years ago and am familiar what what it sounds like).
Any ideas on what it could be, or how I could better diagnose it? I feel like the fact that it quiets on accel and gets louder on decel should really narrow it down, but I don't know what it is. I'm afraid it's piston slap. Rocker noise (loose rocker) wouldn't change based on accel/decel, right?
 
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Does it have the original OPDA? Can you isolate the location to the top or bottom, etc?

I replaced the OPDA a couple years ago (Crown), so I don't think that's it. The noise telegraphs and sounds like it's coming from everywhere. It sounds more substantial than valve train noise and less substantial than rod knock, if that makes any sense. It's loud enough that I can hear it with the hard top on and the windows up.
 
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I replaced the OPDA a couple years ago (Crown), so I don't think that's it. The noise telegraphs and sounds like it's coming from everywhere. It sounds more substantial than valve train noise and less substantial than rod knock, if that makes any sense. It's loud enough that I can hear it with the hard top on and the windows up.

a video might help.
 
At idle, shine a bright light on the entire belt path and fan blades to look for unusual movement. Remove belt and rotate pulleys by hand and feel for play/drag. Timing chain loose?
 
I replaced the water pump and timing set when I did the lifters last winter. I don't see any unusual movement in the belt path.

I found my automotive stethoscope, so I spent some time poking around. The noise is not coming from the top end/valve train area. It's also not coming from the accessory drive. With the stethoscope, the noise is loudest at the OPDA, and less loud on the block surrounding the OPDA. I was unable to easily get any lower than that on the block. This noise is totally different from the howling my original OPDA made when I replaced it. Do they knock like this sometimes when they fail? This is a Crown unit.

Here's a brief video I took of it at idle, with a couple quick revs:
 
I replaced the water pump and timing set when I did the lifters last winter. I don't see any unusual movement in the belt path.

I found my automotive stethoscope, so I spent some time poking around. The noise is not coming from the top end/valve train area. It's also not coming from the accessory drive. With the stethoscope, the noise is loudest at the OPDA, and less loud on the block surrounding the OPDA. I was unable to easily get any lower than that on the block. This noise is totally different from the howling my original OPDA made when I replaced it. Do they knock like this sometimes when they fail? This is a Crown unit.

Here's a brief video I took of it at idle, with a couple quick revs:

are you sure you don't have a Cummins engine ? :) how many miles on it ?
 
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Similar story, several years ago my son said his GC 4.0 knocked when cold. So the next time he did a oil change, he dumped a can of seafoam in the crankcase. Big mistake! The knock got worse till a week later it was hammering bad. I dropped the pan & found pieces of piston skirt. I ended up pulling the head & pistons, ran a ball hone thru it installed new pistons, rings, & rod bearings. 170000 miles.
 
Similar story, several years ago my son said his GC 4.0 knocked when cold. So the next time he did a oil change, he dumped a can of seafoam in the crankcase. Big mistake! The knock got worse till a week later it was hammering bad. I dropped the pan & found pieces of piston skirt. I ended up pulling the head & pistons, ran a ball hone thru it installed new pistons, rings, & rod bearings. 170000 miles.

So the seafoam broke the piston ? I did the same thing and my piston didn't break and it fixed my knock ! 191k miles....
 
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I have 235,000 on my 97 4.0 and it does the same thing, although a little less. It starts up real quiet and then the lifter noise starts. No knocking so that is good. My mechanic says it is time for a new engine. When it completely warms up the sound goes away and the engine is completely quiet. So, I always try to let my engine warm up when cold to extend its life. If I stop for awhile and come back, it is completely quiet as long as it is still warm. If my oil gets a little low, the sound gets much louder. So, I always try to make sure that I have plenty of oil in my engine.
 
You could pull the pan and look at the pistons skirts before taking the motor out
I think the sea foam removed all the carbon on the pistons. Hence it got louder. It didn't break anything.

One thing I see. I believe your only supposed to put like 6 oz. In it not a whole can. And it's best to add it 3 or 400 miles before it's due a oil change.
 
One thing I see. I believe your only supposed to put like 6 oz. In it not a whole can. And it's best to add it 3 or 400 miles before it's due a oil change.

Yep, he added a whole can, then drove 100 miles. Then changed the oil. But, I think it was close to failure already 😕. After the new parts, ran great, no noise & no oil consumption! Now has over 200K.
 
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I'm trying to diagnose a loud engine rattle on my 2005 4.0L 6-speed. Here are the characteristics:
  • It begins about 20 seconds after a cold start and quiets down significantly (but doesn't completely go away) after the engine is completely warmed up (10 mins or so, at 200F)
  • Sounds more substantial than lifter noise (I had lifter noise before and replaced the lifters to remedy it, so I'm familiar with the sound)
  • Even when cold, it does not make the noise when the engine is under load/accelerating.
  • It gets much louder at idle and when decelerating.
  • The noise does not change when the clutch pedal is pressed (it's not the throwout bearing, as I've also replaced that a couple years ago and am familiar what what it sounds like).
Any ideas on what it could be, or how I could better diagnose it? I feel like the fact that it quiets on accel and gets louder on decel should really narrow it down, but I don't know what it is. I'm afraid it's piston slap. Rocker noise (loose rocker) wouldn't change based on accel/decel, right?

Mine rattles on startup or high rpms. I have no exhaust mounts. They are both broken off and the exhaust rattles against my hitch.
 
Novak Conversions Jeep Wrangler TJ radiator