Millions of Jeep 4.0's run regular old oil with no issues. That being said, I have a big cam with high pressure springs, so I run high zddp oil (Valvoline vr1). It's inexpensive insurance anyways. I recommend high zddp oil instead of additive. If you are getting noise from that though, it's too late.
Anywho, you would need to start pulling main and rod caps to check them unless they were super duper screwed up. Do it one at a time and inspect the journals/bearings. Reinstall then move on to the next.
EXTREMELY IMPORTANT--Keep them the same orientation. Do not mix the up. That's why I say do one at a time then reinstall. I scribed arrows and numbers on mine so I can never mix them up.
When you reinstall, make sure you torque to proper spec.
All the bearings should all look smooth and silver'ish. If you see any scoring or copper showing, that's your problem. You can Google examples of spun/scored bearings or journals for examples.
Do you have a torque wrench? If you already had a rear main seal leak, now is the time to fix that. Oil pump is easy to change at this point too if you feel the need.
Hey thanks for the input on the ZDDP. I think I'm going to start using that as well from now on, just in case. As you said, seems like cheap insurance.
Ok, thanks a ton. I was worried that I may mess something up if I started pulling the bearings. I did go ahead and take the girdle off because I knew I would need to do the rear seal, and I went ahead and took the nuts off for the bearing on #6, but I can't for the life of me get the cap off! It is on there so solid that I can't get it to let go. I will keep working at it.
I'm glad I made the right choice to go ahead and take a look at them, thanks for the confirmation on that. I do need to change that main real seal anyway, so I knew I would need to at least pull that last main bearing cap, so I figured I may as well pull at least one of the connecting rod caps as well. I think I will check at least 4,5, and 6. There was no noise at all coming from the front of the engine, even with the stethoscope, so I think I will leave 1,2, and 3 alone.
I do have a torque wrench and I got my hands on a service manual and I found where it has the step-by-step instructions for replacing the bearings, including the torque specs, so I should be good there.
Thanks for explaining the color! I will admit that it freaked me out just a little when I first saw it, even after watching countless videos on YouTube on how to check bearings for knocking! Lol.
Ok, I think I will head back out and see if I can get those caps off. I will do it one at a time like you suggested, thanks for that. I did remember that I need to make sure I keep them all super organized so everything goes back on the way it came off. I'm a little nutty about stuff like that so I should be ok (not a mechanic, so I have some healthy anxiety around stuff like this that helps me keep everything in place! Lol).