Ok guys, I've got a question for you.

I bought my 2000 Cherokee with the 4.0 a few months ago, 150,000 miles on it. All was quiet with the engine. I changed the oil shortly after buying it.

1. First oil change I used 5 quarts of 10w30 with 1/2 qt STP and 1/2 qt of engine sealing stuff (kinda thick). The engine had a "rattle" in the lower end afterwards but only on cold start ups. I ran it for a month then changed the oil again.

2. Second oil change I used 5 1/2 quarts of 5w30 with 1/2 qt of Marvel Mystery Oil to help clean it up perhaps. This seemed to quiet the lower end noise but gave me some valvetrain ticking on the top end all the time. Thinking the oil was now to thin I changed it again a month later.

3. Third oil change I used 6 quarts of 10w30 high mileage semi synthetic oil. Now I'm back to the slight lower end "rattle" on cold start ups. By the time I get to work it quiets down. (3 miles away)

The noise is only at idle as far as I can tell but it still bothers me. This seems kinda backwards to me with the "thick" oil causing lower end noise and the "thin" oil having upper end noise.

The first two oil changes I used dino oil and the third I used semi synthetic.

The engine runs great but I would like it to survive for another 100,000 miles.

Any suggestions? Should I just keep using the 10w30 semi synthetic high mileage oil?

 

i have always used 10-30 in all my 4.0's

 

Oil is personal preference. It gets over-analyzed frequently.

Your 10-30 high mileage is fine. Skip the additives.

Use the proper viscosity for the environment.
*Primarily above 60 degrees farenheit: 10-30
*Primarily below 60 degrees farenheit: 5-30

A little noise in the 4.0 engine is not at all uncommon. My suggestion to you is this. If your oil pressure numbers are in spec (see below) Consider it a "characteristic", more than a problem. You might have this exact same noise 100k from now.......

Oil pressure spec. for the Jeep 4.0:

*Not less than 13 psi at HOT idle
*Between 37-75 psi over 1600 rpms

 

Try a little seafoam in the crank case, helped quite my motor down. And idt I've ever herd a 4.0. that didn't rattle or make some odd noise.

 

Oil pressure is in the normal range for all three oil changes so far. Obviously a little higher on the first oil change with the 10w30 and stp/stop leak.

After some more observations I noticed the "rattle" does happen at every start up whether hot or cold. It still goes away when I get to my destination though.

I realize these engines always seem to have something to say but was just curious if I could make it quieter or go away completely. I really don't like engine noises especially when it was quiet when I bought a few months ago.

Does it sound like the oil pump is taking awhile to prime perhaps with the 10w30 compared to the 5w30?

 

Impossible to know if the PO used thick oil to quite any noises. I agree with the others that suggest using 10w30 (summer) 5w-30 (cold weather). Regular oil changes may quite the engine over time. If your oil gauge shows pressure after 1-3 seconds I think your oil pump is fine.

 

Ive had two high mileage Cherokees that did this same thing(noise that sounds kinda diesel sounding down low, like run,run,run,run,run...), after a thick oil change. Both thick oil changes had a quart of that Crap Lucas that I will never use again because of those noises. Both of those Jeeps are gone now, but I know both owners, and nothing happened to either of them. I know, its annoying, especially when the engines didnt make the noise when you first got them. I even called Lucas up and chewed them out for the noise their 200w oil apparently made. One of those Jeeps did stop making the noise, and was and still is being driven hard to this day nearly 100,000 miles later. Both Jeeps have over 250,000 miles on them now, so Try not to worry.

 

Update:

Fourth oil change: I went with 6 1/2 qts of 5w30 high mileage oil and an oversized oil filter (Motorcraft FL1A).

My noises are gone and oil pressure is still normal. I guess my Cherokee likes the 5w30 so that's what I'll stick with.

 

4.0's are known to have some piston slap. That would explain it being there at start-up and gone within 3 miles. Piston slap is caused by the pistons being slightly small for the cylinder bore, usually when cold. As the engine warms up the aluminum pistons expand at a greater rate than the iron block, therefore becoming "larger" in the bore and reducing the clearance and associated noise.

 

4.0s were known to make noise, and IIRC, about 1996 the block was strengthened to reduce the noises.

My oil pressure shows a little lower than I would like, so I'm going to hook up a real guage and see what numbers it shows. I'm also due for an oil change and have Mobil 1 10-30 high mileage synthetic and a M1 filter waiting. Had I known that I could use the larger filter I would have gone that route.

 

I've always used Mobil 1 10W-30. IMO additives are not as necessary as using good quality oil changed out at a reasonable interval.

 

I changed my oil yesterday. It had Pennzoil 10W-30 synthetic and ? filter from the local garage about 5500 miles ago. I used Mobil 1 10W-30 high mileage synthetic and the M1 equivalent of FL1A or PH8A. My oil pressure shows 5-10psi higher than it did with the previous filter. The FL1A is a larger filter, probably twice the volume of what had been on there, and probably twice the volume of the M1 fliter spec'd for the 4.0. I still want to hook up a mechanical pressure gauge and see what pressure it shows.