Hi All, I've been having trouble finding anything that pertains to myself on this topic, except maybe the flexplate bolts, or it's cracked, but I wanted to get some opinions and things to check.

It's cold here in Michigan, and yesterday I started up my 97 XJ to warm up a tad while I moved my girlfriends car. When I got out of my jeep I hear a pretty noticeable knocking. Didn't here it when I was in the cab, so I'm not sure how long this has been going on (unfortunately). I also didn't notice it when it was hot out over the summer. Stuck my head under it and couldn't tell exactly where it was coming from. The sound goes away after just driving for a minute or two. I don't hear it on acceleration, or at idle once it's warmed up.

Background - 97 Jeep XJ, 4.0L I6, 64,000 miles (bought with 56,000). Bought back in late April. Drives nice and is quite for the most part. I'm not exactly sure what type of oil was used in it before, but I have been putting Mobil 1 in it since I've owned it. I think it was a little gunky because I kept having to change the oil filter because I'm pretty sure it was getting gunked up and disturbing flow because my oil pressure would get low. Change the filter and back to normal, and it's been good since the last time.

I don't have any smoking, overheating, leaks, or anything of that nature. Oil pressure sits right around 20psi at hot idle, and beteween 40 & 45psi while at speed or accelerating. Also, the oil pressure does move slightly (I've only noticed it at idle). It isn't bouncing fast or moving all over the place, but it does move up and down a couple psi. Sometimes it doesn't even move the couple psi, and sits steady until back on the accelerator and then it's right back up to between 40 &45 psi.

I would truly appreciate some things to check as I don't want any serious problems to occur.

 

yeah. mine has been doing it for years. i have a 97, 2.5 liter. coworker has a 98, 4.0 and does it when it is cold here in maine. just takes a bit for the cold oil to get flowing. i would not worry about it. put a good oil filter on it. i use the napa "gold" filter and plain 10w40 castrol gtx oil every 3,000 miles. used 10w30 weight oil one winter. did not seem to be better.

 

Your oil pressure is fine. When you changed out the filter, What brand did you have on it and what brand filter did you install. A cheap brand of filter can and will cause a knock on a cold start. If you have a cheap brand such as Fram or any other cheap made filter replace it with a Napa Gold, Wix or Mopar and see if it halp with the knocking.

 

This^^ first.

 

I've been using a mobil 1 oil filter. Figured I would keep brands the same. I'm not exactly sure what filter I took off. I'm pretty sure it was put on by an oil change place, so something conventional.

I tried to listen to it a little more when I left work, turned it on and I actually could hear the knock in the cab. Literally put it in reverse, backed out, put it in drive, drove down the street maybe 500 feet, turned the radio off, and couldn't hear it anymore.

I just wonder how long it's been doing it. It very well could have been doing it during the summer, but since my radio is on I just never noticed it. It's definitely a noticeable knock, but like I've been saying, it only happens at first start up. When I was driving home it was driving real nice (even with it being 25 degrees). Even turned down the radio and didn't hear anything. She was purring like a kitten.

*Edit* Also I've always used 10w30 all year round without issue. (had a 2000 4.0L for about 5 years) Even last winter with it being like 0 degrees all winter it was fine.

 

could be a exhaust leak. i had a different knock about a year back. the back bolt on exhaust manifold broke off. lucky for me got it out with vise grips and put another one in. anyhow, sounded like a knock also and stopped when manifold heated up. but, got steadily got worst.

 

How close are you to oil change time? Mobil1's 10w30 is thicker than most 10w30s. It's supposed to have 5w in it.

 

I'm actually about 2k away from another oil change.

It was not happy this morning. It is like 10 degrees out though. I don't even know how to explain it. It started up, but it was like something was frozen, and had knock itself loose. Once it warmed all the way up it was fine, but it is damn cold, and I know XJ's really aren't much of a fan of that.

I'm thinking the cold has a lot to do with it because none of this stuff happened until it got this cold out. I just worry because its only November and there is a lot of cold weather and winter to go.

 

Time for an oil change with new filter my friend. Any filter can fail. At this point your Jeep's signs warrant some action. Check the old oil for anomalies like chunks or water.

 

Chunks of what? sludge or metal? Wouldn't it run rough if something like that was wrong with it? Like I said it wasn't happy when i started it, but once it was warmed up it was fine.

I obviously want to get it figured out, but I'll be pretty damn pissed off if the I6 is ****ed up on me!

 

Try this.

First, shut the radio off.

Start the engine. Hear knock? Shut it off. Wait 10 seconds. Restart. Knock gone?

 

Sounds like piston slap. It gets worse in cold weather b/c thermal dimensional differential between the cast iron block and aluminium pistons are greater. Aluminium is a very good conductor of heat so combustion temperature heats the piston rapidly...500 feet.

 

I'll give this a try when I take off for lunch and let you guys know.

Is piston slap a problem, or is that just a cold weather deal?

I'm also worried about what salad said now. I never noticed any **** in my oil when I've drained it before. What happened early this morning was weird and I've never had anything like it happen before.

 

No, normal in alot of engines. Just drive easy until engine warms up a bit.

 

I had problem like this in my 98 tj. it ended up being the #4 piston broke right up to the oil ring and would cause really bad piston slap. If you have the means I would pull the pan just to make sure. I have 248,XXX miles on my xj right now and have very little piston slap. There have been a few cases that I had read about over the years with the skirt breaking on some TJ's, ZJ's and XJ's. I guess Chrysler had a problem with castings at some point but not enough to warrant a recall.