Need Help

[GMan]

Hello: Have '96 XJ 4.0 liter. Has been running hotter than normal 220-230 last several months. Now there is a low rumble from the motor on start up that goes away after motor is to normal operating temp. Anyone have this problem?

Thank you GMan.

[bluedragon436]

With the low rumble that goes away I'd say possibly your exhaust manifold seal or possibly even the usual cracked mani... but with the cracked mani wouldn't think it'd go away really... For the overheating I am thinking a head gasket possibly.... have you checked your oil and your antifreeze to see if either look like they've mixed at all??

[DETOURS]

^....Yea, that.

[GMan]

Thanks. Went over the manifold carefully, nothing. Oil is perfect, clean and clear, no gray.

[bluedragon436]

hmm.... that is a bit odd... I'm still almost thinking that the seal for the mani at the head is leaking a bit... cause that would cause quite a bit of exsessive heat to heat the outside of the head where the sensor is.. Only think that because that is what we found on a co-worker's YJ when he was having a random overheating issue with no loss of compression or oil/coolant mixing

[GMan]

checked carefully for pipes knocking the frame etc. cant seem to even get a bead on what to do next. Engine is well taken care of, clean etc. Anyone with experience with an engine stethescope?

Will recheck manifold.

[GMan]

you might be right. will recheck manifold. your co workers xj problem is a clue. I will run with that for now and let you know.

[NW99XJ]

Think about a compression test, just to see where you're at as far as that goes.
There may be a possibility that you have a plugged up Catalytic converter...that too could cause some minor over heating. Double check to make sure your clutch fan, and aux fan is working properly. (I know some this may see redundant)
The oil passages in Cherokees lend themselves to drain the upper end overnight or after a period of sitting for a while...it then takes a little bit for the oil to reach the lifters, etc.. after start-up.... hence giving the 4.0 a sound like a tractor when its started up sometimes. Oil stabilizers will help with this in some cases. (not saying this is your issue)
Now when you say "low rumble"...to me that doesn't sound like the "clacking" sound that would normally be heard with a sticky lifter, low oil pressure, or an exhaust leak.
There still could be an exhaust leak in your manifold, its just in the backside of the collector where its almost impossible to see. This is the "typical" location for them to crack.
Another thing to look over real carefully would be the motor mounts... maybe the engine is getting a little more movement at start up, and after warming up, the idle smooths out some, and the vibrations are less noticeable. -just shooting out ideas here.
make sure things like intake/air box and hood hinges are secure, and that the battery is properly held down. Anything that can come loose can cause noise/vibrations that are undesirable.
I'm sure there's more that I can think of, for you to look at, but as i'm typing this its still pretty early, and I haven't had my coffee yet.....
So I hope some if this helps at least somewhat.
Good luck!

[GMan]

all good ideas, very much appreciate all of your thoughts. Will do all of them and let you know.

[4.3LXJ]

Also check all manifold bolts. A slightly loose one can give noise on start up that goes away when warm