Hi everyone. I own a 1996 Jeep Cherokee with the 4.0 I6, automatic. I’ve noticed what might sound like a rod knock, but it seems to go away after its warmed up, and hasn’t gotten any worse over the months I’ve been driving it. Oil pressure is good, about 40PSI when warm at idle. This noise also just seems to be random, as it makes the noise, goes away for a few seconds, comes back for a second, goes away, and so on. It’s never constantly making that noise, but instead just randomly makes it, again pretty much only when it’s cold. Could it be the flex plate bolts? I know those are known for coming loose and making a rattle, but not this kind of rattle. Everything else seems tight, such as the manifold bolts. If anyone has any idea on what this might be, please tell me. It’s also important to note that the engine has been really well cared for, even at 186K the cross hatch marks are still on the cylinder wall. I also took the Valve cover off a while back and there was ZERO sludge, so I don’t really think this is an oil problem, but your guess is as good as mine. It also doesn’t seem to really go away when you rev it up.Thanks to anyone who replies!!

 

It could be piston slap or something simple. Get a mechanics stethoscope and poke around.

 

X2 on the piston slap. My 92 makes a similar noise and has for quite awhile in similar conditions.

What type of oil do you use?

 

Much more common:

https://www.cherokeeforum.com/f51/ho...ocking-125547/