Again, wouldn't this be something that is constant and knocks all the time if I had a bust piston? It drives fine once it's all warmed up. I would think a busted piston would be a major problem and my xj wouldn't be driving all that nice once warmed up.

 

You are right and if the piston is broken it will knock all the time, but if your piston slap is that bad right now you might have a piston ready to go. That is how my TJ was acting before it was a constant knock. Then I pulled the pan an saw there was chunks of aluminum in the oil. I would also look into the possibility of a rod knock that only shows itself when the engine is cold and the oil has not reached the bearings yet. I had the same issue with a Subaru. It had a rod knock till the oil pressure was up then it was fine. This might explain why the motor had to "knock something loose" when it was starting. If it is a rod bearing, that piston could have been at the bottom of the stroke and got stuck and have to be knocked loose to move again. I would pull the pan and have a look around I know you don't have many miles on the jeep but they could have been really hard miles from the previous owner.

 

As far as I know the jeep wasn't driven a whole lot except for trips up north. But I guess you can say anything when you are trying to sell a car. I never heard any abnormal sounds when I test drove it a couple times. Drove like new, but then again, the OP could have always let it run for a few minutes before I got there. I guess I'll never know.

Not sure if I really have the means to drop the pan. Is it as simple as removing the bolts, or is there more to it than that?

 

Mine has had piston slap since I bought it about 50,000 miles ago!

 

Yes and no. The best way to to it would be to remove the exhaust pipe from the front of cat to the bottom of the exhaust manifold. This will give you the best access to remove the pan. It can be done without removing the exhaust pipe but it is pretty tight in there. And if you don't have a lift on your jeep you will have to drop the axle out of the way a little for better access as well. Just be care full there are 2 different bolt sizes on the oil pan there are 2 in front and 2 in that back that are bigger then the rest.

 

Yes. Do what I recommended first before going off the deep end on this please.

 

Hey Cruise, I did give your recommendation a try, and didn't seem to see/hear any change when I turned it on the second time.

Yesterday after work I had a good buddy of mine who is constantly working on vehicles give it a look. Of course it wasn't cold when I got there and he said it sounds like its running great. We did some work on his LeMans to let it cool off as much as possible. Came back turned it on and you could hear it slightly, since it wasn't completely cold (was sitting at right about 50 or 60 degrees), and it went away fairly quickly because it easily warmed up. He thinks it's just piston slap and not to worry.

This morning I still heard it when I started it up on a completely cold start, but it didn't seem as noticeable as yesterday (weird), but maybe I was just worrying more because of the "frozen" deal I explained yesterday. I think I'm gonna try and not worry about it and just keep listening to it to see if anything changes. It also didn't do the "frozen" thing I talked about.

Also you can hear it much more from underneath than above. I'm thinking maybe flexplate bolts?

 

Never a bad idea to check the flexplate bolts and get them handled anyway.

 

I've had my 2001 for about a month and mine does the same thing. Only for about 15 seconds, or less, and it goes away. So I changed the oil with 10W30 full synthetic and put a WIX filter on it, but it still does it. There's a list of things I will look at but it's been too cold.

 

Piston slap takes place in the bottom of the cylinder. Since the bottom of cylinder is facing down into oil pan it acts like a megaphone directing the sound into the lower area of the engine.

 

I would say mine does it for more than 15 seconds, but It goes away fairly quickly once I start driving and oil starts getting pumped through everything.

I'm gonna check out the flexplate bolts just to make sure, but it's been damn cold here in Michigan. I don't think I'm gonna worry much.

Yeah, I'm thinking it's just piston slap.

 

Just FWIW these engines are tanks and most of them in my experience make knocking/ticking/tapping noises. Mine personally has 292k has always had a cold weather knock at start up for over 180k. Its had a significant tap in midrange rpm for at least 8k but starts and runs great no smoke and just a small valve cover leak. I wouldnt worry terribly about it at this point unless you start getting more consistent signs of a problem. Ive seen other members with pretty significant knocks and continue to run fine for 10s of thousands of miles and beyond.

I intend to replace my engine in the not to distant future and have considered a reman and I will not be surprised or alarmed once its installed that it has its own knocks in various weather and conditions.

 

Hey gents, new question and again, hope someone catches this post.

This has only happened to me twice, only lasted for a quick minute, and this was on Tuesday, and Thursday of this week. I heard a knocking/tapping noise when my XJ was ALMOST completely warmed up, and only heard it when I was lightly on the gas. Then after a minute it went away. It sounds like its coming from the passenger side.

I've pretty much determined that the knock I originally posted about is just piston slap. But this one is different. Again, If this was a rod knock I think it would have gotten worse at this point and been more constant (wouldn't only happen sometimes) as I drive a half hour (all highway) to and from work every day (so an hour total).

I have 65,000 on it and I don't think a tuneup has ever been performed (spark plugs, wires, distributor cap, and rotor). Any chance that since this only happens once and a while and doesn't last very long at all it could be a spark plug or wire? Or maybe even the sensors around the throttle body? Maybe that is relevant to any knocking/tapping, but thought I'd ask.

 

Can you pinpoint where this knock is coming from? Get a mechanic's stethescope thing for a few bucks.

If it's towards the top of the valve cover, it might just be lifter tick. How you describe it - only happening when revving a bit and then it goes away, I'd suspect the ole' lifter tick that most of these get. Mine gets it when very warmed up and then idled for a long time, and goes away again.

Just a possibility. You need to do some more diagnosing, ie pinpointing it.

 

Unfortunately that's the problem! When I'm sitting at idle (park or drive) the sound is gone. It didn't go away after revving for a second, It stared out of nowhere and I could only hear it while on the gas, then it got quieter and was gone after 1 or 2 minutes (this is what happened Thursday). The first time it happened (Tuesday) it happened out of nowhere as well when I was pulling into a parking lot. I parked, did my thing, left the store, and the sound was gone. Both times I heard it I noticed the XJ was almost warmed up but not completely (maybe 180 or 190 degrees on the temp gauge).