mike.2492

I have a 94 XJ, 4.0 with 145,000 miles. I chaged the oil, with valvoline high mileage 10/w30 synthetic blend and some lucus oil addative and the engine developed a valve tap(or whay I think is a valve tap). It is loud duirng warm up but can still hear it after the engine is warm. The noise seems to be louder under the engine when it is warm. As far as a valve tap, I checked the oil level and it was good. Some people told me it might be a sticky lifter so I did the sea foam treatment and it was no help. When I replaced the oil again, I used a 10/w40. It did not help. I removed the valve cover to check the rocker arms and push rods, they were all ok. Does anyone have any suggestions on what I should do nextor what the problem might be. collapsed lifters? sticky valves? oil pump?

OverlandZJ

You have an oil pressure gauge in the dash cluster? What's it reading cold and warm at idle?

mike.2492

No I have the SE which only has a low pressure warning light. Suggestions on testing the oil pressure.

OverlandZJ

Know anyone with a good assortment of test equipment? Local shop? Try asking them if they can throw a mechanical pressure gauge on to check the pressure.

It may not be your problem, but eliminating it would help your troubleshooting.

mike.2492

ok thanks, I will check around.

1991Jeep_Man

Just a Jeep being a Jeep lol. Mine does the same thing... Jeep tick

00xj-classic

my 2000 KNOCKS until it warms up..

Zreiser

From what I understand (thanks to the gurus here), knocking is common, especially if you added synthetic oil...that could be the source of the problem. You gotta use stuff that the engine is used to/designed for or you create problems for yourself. Go back to real oil, try 5w30, that's what I was recommended. I haven't done seafoam yet, but I did add sealer of some no-name brand when mine was low on oil, and the heavier oil, and knock went away until I stupidly added lighter weight oil the next time (duh!).
You might end up with a problem if you have metal shavings in the oil when you change it, but other than that, you should be fine for a good long while.

djb383

Oh my, here we go, another synthetic oil myth and thicker/heavier is better.

00jeepXJ

Yep... my 97 sounded like a diesel when it was idling.

djb383

From what I've seen/heard, the Jeep 4.0 is somewhat of a noisy little motor. Ours, at just 48K miles, has some ticks and noises but it runs like a top.

cdeal28078

I just acquired a 1990 Cherokee my dad bought from an auction. It was a total loss sell so it was totaled out and rebuilt. I found a paper in the glove box showing a long block replacement 35k miles or so ago so was happy about that. Thing is it has a small knock at idle and I can hear it going down the road. I finally got my mechanics stethoscope out and tracked the noise down to the exhaust donut where the manifold hooks up the the exhaust pipe.
Seen it a lot of time where a truck where have an exhaust leak and it sounds just like a valve tap
Get a piece of vacuum or fuel line and stick one end in your ear and move the other end all around the engine while it is running and see if you can track down the problem
Works very good
clint

XJ30188

Most likely the lifters, seems to be a common problem in these.