15XJ

Hoping someone has a little experience with a different knocking sound from the famous 4.0 inline 6. I will provide the best details I can to make this easily diagnosed the first time...

94 XJ limited. 180k miles, odometer reads higher but the speedo has been 10% high from the tires for the last 3 years. I just got this, guy overall seems like he was a bull****ter.

Issue is; at stone cold start up, I can BARELY here a "ticking" sound, as the video will show you, it GREATLY increases in noise once the engine is fully warm. There is no noises that concern me at idle, when cold. This sound starts from 1750 RPM and up. Haven't ever revved it past 4000 roughly.

The cold idle is 60 psi oil pressure. Hot idle pressure is 40-45.
The plugs are clean, compression is good, cannot hear or feel any exhaust leaks at the manifold. This all seems confusing because mostly what could be wrong, should be louder when COLD not louder HOT.

Any thoughts here? Rockers are tight. It is a manual transmission, everything feels great there. I've done a ton of searches, can't really find anything that specifically pertains to this issue. It's leaking like a son of a ***** from the pan and rear main.

It's one thing to scrap this longblock and put in something new, another if it's fine to repair these leaks.. Engine is BONE stock except the muffler was swapped out. No smoke at start up, has good power considering it has 33's and lifted 6".

VIDEOS:

This video is kinda crappy. Hard to get the sound and no wind noise with a cell phone. You can hear it when I'm in neutral, and when I first take off in first pretty clearly.

This video is from neutral, the noise is super clear and almost pronounced at the very end as it comes back down to idle.

Jooman07

To me it sounds like maybe a lifter. Mine makes that sound on a cold startup however. One of my lifters is sticking just haven't tried to figure out which one yet. Someone suggested putting some marvel mystery oil in the see if that helps.

15XJ

I actually have a bottle of that I purchased yesterday. The dealership said try stuff called valve doctor that I couldn't locate around here.

I'll give it a shot. Worth the $5 gamble at this point. If it were a lifter though, wouldn't warm temperature and thinner oil quiet the lifter versus make it louder?

Almost seems like it is a bearing that's pissed when the oil thins out. I tried using a stethoscope but can't really get anything definitive.

Jooman07

Like I said mine makes the same noise on cold startup. It may or may not be a lifter. It just sounds similar. Does it sound like it's coming from the top end or bottom end?

15XJ

Well my passenger heard the noise louder on the drivers side. I crawled under it and it sounds like crankcase. However on the outside it's more pronounced from the drivers side, like a header.

Header gets hotter and expands revealing the crack? It's a nice theory but I couldn't see or feel anything.

Jooman07

I guess it's hard to tell exactly what the sound is from the video. Your theory makes sense but testing it is another story. Not like using soapy water on a tire to check for leaks. It'd burn off in no time. You might could look and see if there is soot from rich exhaust anywhere on the manifold but then you might just be chasing non existent things and wasting time.

15XJ

Oh I hear you. I can turn a wrench if need be, just not much desire there. I bought this and the seller was dishonest and I'm left with my *** in the storm.

I'll maybe pull the manifold and inspect it closely. If I don't find a crack I guess I can just keep on pulling.

15XJ

Well, made a decision tonight.

It needs an oil pan gasket and rear main badly. It might be bottom end or who knows. Either way, if I'm pulling the transmission out, the whole thing is coming out.

Buying a new longblock for $400 with 110k miles and good compression. Putting new seals and gaskets in the ***** and calling it a day. Figure for $400 and I'll sell this thing for $200 and actually tell someone that it's making noise. Won't cost me much more then just replacing the gaskets on this current engine.

Unless anyone else has any thoughts based off these videos?