The 4.0 has about 270k on it, and runs strong.
When the 4.0 L is cold it has a ticking noise from the top end which I think sounds like a lifter stuck, and when it gets over about 160 degrees the tick goes away. I usually warm up the engine when it is cold and drive it after the tick is gone.
Also I was thinking maybe an exhaust leak which is sealing itself when warmed up.

From the forum a lot are suggesting Marvel Mystery Oil.
Searching the web shows research claiming that it could damage your engine from over cleaning it and breaking down the oils properties.

How many of you Cherokee owners have used Marvel Mystery Oil (MMO) in the crankcase and what kind of results did you find?
Any success stories that MMO cleaned up sticking valve lifters?

 

marvel oil has been arund for years its good stuff they do make other treat ment that works the same way do some research and ust what you fell good with

 

I've heard alot of people suggest Sea Foam. Never used either myself, though.

 

ive heard alot of things more about sea foam being bad than the others

 

The lifters are down low inside the block on the passenger side, rocker arms are on top under the valve cover. Removing the valve cover and re-torquing the rocker arms could eliminate/lessen the noise. The 4.0L is not known as a quiet engine.

 

Indeed. They are actually known to be quite the opposite.

Most expect the ticking and such.

 

Well is it a normal tick or abnormal? All engines make the usual ticking noise.

 

Normally, our's ticks all the time......, so would that be abnormal? LOL

 

Quick questions, is there anything else I should do when I do the valve cover gasket? Like do the valve clearances need adjusted on these engines?

After I fixed my manifold leak I can hear how loud the actual engine is and I don't like it

I'm gonna give it seafoam thru the intake, a motor flush, then oil change and put some restore in it and some lucus in the gas.

 

No valve adjustment. Just torque the rockers at 21 ft/lbs. Check me on that torque spec.

 

I guess from what others are saying on the forum the 4.0 usually has a lifter/rocker arm tick and is considered normal. I guess I am blessed that mine stops ticking once the engine warms up.


The questions at the beginning of this post had to do with Marvel Mystery Oil and if anyone has had any luck with it cleaning up sticking lifters or is this stuff just modern snake oil as many experts claim.

Anyone have any real experience with MMO?

 

What's it look like when u remove the oil filler cap?

 

I was thinking about this for a bit, and I too have heard bad things about sea foam. But more often than not I hear the bad things are a result of improper use.

 

I used seafoam the fist day I got my Jeep it barley took a 3rd of the can what I do is take it pour it into a cup then use a bendy straw to the vacume line until the engine knocks like crazy or shooting out white smoke. Let the engine sit for 10 min then drive like an ahole. No joke that's how you get the crap out you don't have to go to the highway just enough to push it threw your manifold. Every car is diffrent for seafoam the exploders take the whole can then it starts to work.

 

yea, I gave up saying it but I will again.

I've used seafoam through the intake on every car I've owned and tons of friends cars, never had anything but good results when done right. I used a half can in the jeep.

It can sometimes foul your plugs or o2 sensor. I usually do it before an oil change and plugs.