Tap Noise

I have a bit of a problem or rather an observation that i need to know if i should worry about. I have a 94 xj and whenever i start it it sounds like a really loud diesel. I understand this is normal but under closer inspection the cover on top of the engine (i think valve cover), it sounds if someone is tapping on it. Its been like this for a while and was wonderig if this is normal ?

pete

You're probably hearing cold start piston slap which is indeed normal, but on high mileage engines rocker wear or sticking lifters can also cause similar noises. Give the crankcase a good flush by adding one quart of ATF with some fresh engine oil. Run it for about a week and change the oil again with a new filter. By then the ATF should have scoured the engine's insides clean. Just cross your fingers and hope that old gaskets and seals don't start leaking.

A friend recomended i empty a quart of oil and put in a quart of marvel mystery oil about 200 miles b4 an oil change and run in it thru those 200 miles and then empty all the oil and put brand new oil in.

is this good..or just bs.

pete

I've heard that marvel's mystery oil is very good though I haven't had the chance to try it myself.

If the tap is a metallic one that goes right away as soon as you're well started, it could be just lifter noise, and if so, the Marvel mystery oil might help (cuts carbon, supposedly). So might a couple of ahead-of-schedule oil changes with light weight high detergent oil. If it's piston slap, which sounds more dieselish and takes longer to go away, Marvel will do nothing at all for it. Piston slap is caused by pistons that rock in the cylinders, and a thinning, solvent sort of treatment like Marvel will not help. Actually nothing will, but an XJ engine can happily slap away for hundreds of thousands of miles.

A usual characteristic of piston slap is that it will get quieter when the engine heats up and the pistons expand a little.

If you do have a slappy engine, make sure that you keep track of other possible noises. I have found with my 95, which has a persistent slap, that it can mask other noises, such as a failing water pump or bad idler pulleys.

Yeah, my '95 has piston slap and after its good and warmed up it gets much quieter, to the point that I really have to listen for it. I've found a few things that seem to work to quiet it down some. One is Lucas Oil Stabilizer and the other is running a heavier weight oil. I run 20/50 in mine when the temperatures permit. Btw, I've had piston slap in my 4.0 for the last 50K miles and I havent noticed any ill side effects other than the annoying sound at idle.

My 90 had slap when I got it with 101'000 miles on it. It has 204'000 on it now and doesnt sound better or worse and still runs great.

Well when i start my engine after it has been off for a night or so...it is very loud...kinda like a tractor diesel engine...lol...it seems over the years it has got a bit louder but that can be my imagination. After about 10 min of driving it idles a lot more quitely the noise is still present but a lot more toned down.

pete

I guess i will give the marvel mystery oil a try once its closer to my oil change time.

pete

jeepsrock said:

I guess i will give the marvel mystery oil a try once its closer to my oil change time.

pete

Click to expand...

I changed my oil twice in the last several weeks. Firstly changing the oil, and putting in a detergent, then the following week changed again and put in a NAPA silver oil filter. I noticed the tapping noise I'm used to hearing louder than usual. Checked the oil, as I have a small leak somewhere [not positive where it's coming form and it's been two weeks since I did the second oil change] Oil looks pretty good and clean still, and I use Lucas oil stabilizer as well.
I'm just concerned about it being something that is a usual noise I shouldn't worry about, or something I should be worried about. It seems to 'tap' away in time with the lifters. I really don't know the difference sound wise between piston slap, and the lifters. When I stood in front of the car with the hood closed, it sounded like it was coming from the front inside the engine, but when leaning above the valve cover, or inside of the jeep, it sounds more like in the valve cover.
Any ideas what this actually is? Should I be worried something is giong to break? or am I just being overly paranoid? Is there an easy way to know exactly what this noise is? I have to safety it really soon, and dont' want to have to take it in and spend a lot of money on something if I dont have to.
TIA

Yeah, I think you are being a bit paranoid. My old 88 XJ had a ticking/tapping noise from the valve cover and so does my 2000. I figured it's just the lifters and pretty typical of the 4.0L engine. It's not a pretty sound and I've learned to live with it.

Thanks, and don't mind being a bit paranoid. I"ve put a hell of a lot of work rebuilding this, and don't need something on the engine to go. It's run like a champ since getting it going last Sept, and been driving it since Dec.
It's always made some noise, but just seemed louder today. Maybe with the temp being higher? Now that I've got my main oil leak problem fixed I can do normal oil changes and I monitor the colour of it to see how quickly it looks dirty. So far so good. I plan to keep a rigid maintenance schedule on it so it lasts as a jeep should. Being still a newbie with my XJ, I've learnt alot, but don't want to blow something off as being nothing and have it bite me in the ass.

can someone describe the difference between piston slap and lifter noise? I've just had a funny sound appear in my new (to me) XJ.

Occasionally on a cold start (maybe once every three days or so) I get a sound like a ticking clock. extremely loud, it only lasts for a few seconds, and stops abruptly.

Thanks

Ultimate, that's classic lifter noise. As was stated, try a can of Marvel Mystery Oil in it. I cured my tapping with simply a couple of oil changes.