warm engine knock- 92 xj

My 92 xj, 4.0 daily driver has developed a warm engine knock. It wasnt really noticeable until I did an oil change on it. It has an ancient looking purolator filter on it when I did the change. I used a wix napa gold filter and shop bulk 5w30 esso oil. I noticed the knock almost immediately, I added some Lucas treatment to see if It would help, It did not. I swapped in some penzoil 10w40 and a filter, still there. I run rotella 15w40 in my offroad xj but it may be too thick for our cold temps. Why would it know when warm and not when it is cold? Just a jeep thing and don't worry about it?

Mods, move to OEM Tech.

where did I post this? thought it was in oem ? Warm engine knock must be a unique condition I'm thinking...

Oil pressure? If you don't have a gauge on the instrument panel you should plumb in a mechanical one. Hot idle pressure should be at least 13 psi. If the pressure is low that could indicate bearing failure, and I would pull the oil pan and take a look.

Also, is the knock only heard at idle? What happens if you blip the throttle in neutral, does it aggrevate the sound or does it go away? Rod knock should sound worse when you blip the throttle. If it is only at idle, it could be piston slap. My '92 has a sort of knocking sound when the engine is warm, but is only heard at idle. It sounds like a diesel, really. I have 20-25 psi hot idle oil pressure, so I figure this is piston slap, which is supposedly not uncommon on early H.O. 4.0s. It has made this noise for 12,000 miles now without any trouble and without getting noticably worse. My previous '92 XJ had the sound as well, and I put 40,000 miles on it before it was wrecked.

Have you been able to tell where the knock is coming from? With the way you describe the old oil filter, maybe the fresh oil freed up some sludge that clogged up a passageway or a lifter somewhere? If the noise is coming from the head then that's what I'd put money on.

You should also check the rocker arms and bolts, and the flexplate/bolts if it's an automatic.

yes I have a dash gauge, It was low before my change, the old oil came out like water, cold oil pressure and warm pressure increased significantly. Sounds like bottom end to me, but I will check torque bolts/nuts. It doesn't get better or worse with rpm. Maybe try with a stethoscope and narrow it down