My 96 4.0 has 218,604 miles on it. It has a 5 speed trams so no flex plate. It sounds a lot like a Diesel engine at idle to 1500 rpm all the time cold or warm . It has good power and is responsive Other wise. I have tried sea foaming it, the MMO, motor flush all with changing oils. I am running 10w 30 castrol gtx in the engine. I don't see any cracks in the manifold. I tried using a steatha scope to pin point it but did not have much luck. Not sure i was using it right either.

I was thing of taking the serpentine belt off and starting the engine while still cold to see if it was pw steering pump or fan. Is the safe.

I took a video of it try to get the sound it's making.

Any help would be appreciated.

 

No worries running without the belt...I do it all the time and its weird how quiet the motor is without all the stuff up front spinning.

 

When you run the engine with the serpintine belt removed touch the timing chain cover with your stehoscope and listen for timing chain noise.

Remove your valve cover and pull a set of rockers and pivots and see if they are badly scored. Be careful removing and reinstalling the cap screws that you don't twist the bridge. Torque for the cap screws is 21 ft. lbs. Have the piston for the cylinder you are working on at TDC compression when removing/reinstalling the bridges. A scoed rocker/pivot may mean all rockers and pivots are scored.

Replace the valve cover gasket with a Felpro rubber gasket.

People have had good luck cleaning out the oil system by using Rotella T6 5W-40 motor oil with MMO and using a good oil filter, like WIX or NAPA Gold.

 

Thanks for the advice. If you want to take a lisen here is the link
http://s754.photobucket.com/user/Xjo...d7ac1.mp4.html

 

The mech fan should not be I if the engine is cold correct ? Mine is spinning all the time

 

Found the issue the engine is pretty quit with the belt off so I started wiggling the pulleys the water pump has about a 1/4 inch of play in it . That can't be good. The pump only has 50000 miles on it and its a bosh brand so I figured it last as long as factory did. Oh well looks like I have a weekend project

 

It spins when the motor is cold too, just with more slip.
Sounds like you found the source of the noise. That's a pretty good clank going on in the video.

 

my xj is also making this noise. looking forward to your end results so i can fix mine. thanks

 

It was the water pump. It started eating the timeing chai cover, and the inside of the pump it self. It took about 3 hr to change it is quiet as can be now

 

thanks for the reply. looking in to changing mine out