Bluemax

ok, so i got this 91 xj 4.0 about a month ago. engine had a lil noise to it but so do all the other jeep my family has. So i changed the oil in it last night, did the usual like in i do in all the other jeeps 10w-40 with a bottle of lucas. Ever since i did that the noise has gotten worse! what is it?

JeepCoMJ

you should have just put the RIGHT fluid in..

10w30 is factory spec for these motors. there is nothing wrong with it. lucas and other stuff is not necessary, and even harmful.

you have one of 2 problems actually.

either this fluid is too thick, and made your rod and/or main bearings take a dive, or the guy you got the motor from had put gear lube in it to quiet down the noise. it can go both ways, strangely enough.

98jeepsrt6

Have you considered other possiblities rather than the type of oil he used. I put 10-40 in mine and it doesnt sound like a deisel. No extra additives like lucas, etc.

Could be a exhaust leak, one small enough would sound like a deisel. Does it sound like valves? Hows the oil pressure? Does the sound go up with the rpms ? Ask questions before you figure you know it all, and say hey you used the wrong oil.
The man clearly states that he does the same on EVERY jeep in his family and this has never happened.

JeepCoMJ

it is still not the proper oil. says so in every service manual. he's throwing vairiables in that just screw it up. 10W30 and 10W40 motor oils are actually quite a bit different.


and no, I haven't considered anything but motor oil. the problem didn't exist as bad before the oil change, and exists worse now. that tells me that the motor will be needing a bearing set, at the very least, and that it was probably knocking like this before, and the previous owner probably covered it up with gear lube or atf.

alloutperform

ok i wish i was kidding but i had one like this once and i put that engine restore that comes in the soda can looking can and it's been quiet ever since...jeeps still going strong and quiet i put a can in every oil change i do for it (gave to ex girlfriend before she was the ex) lol

98jeepsrt6

i agree with you that it is stated in all manuals, blah. But as the motor gets older it may need a thicker grade oil. Unless you start rebuilding everything to keep it "new and efficient". Not everyone can do so, so as parts wear and tear the thicker grade helps.

I would say we need some more info. Where is the sound coming from, how many miles, etc..

JeepCoMJ

eh. if a motor knocks, it needs to be torn apart. if you don't want to, don't. drive it til it blows.

room mate I used to have bought a '97 xj with no issues other than needing a water pump. we did the pump, drove it 4 hours home, let it sit for a week, registered it, plated it, took it for a test drive, and trans started slipping. drained it, it was ALL lucas trans additive...zero dexron. put more lucas in ONLY AS A BAND-AID to get it going for the next week. changed oil, immediately started knocking and running like crap with the proper stuff.

so. I resealed another good motor, took another good trans, set them up, yanked his 205k mile stuff out, replaced it, and called it good. no reason to spend umpteen hours under the darn thing to figure out what was actually bad.


*shrug* I'm the guy that just replaces EVERYTHING when something goes wrong. and not that I buy new stuff...i replace it with known good used parts and never look back. well, except engines in my personal vehicles...always new, no matter what.

Gee oh Dee

Thats not the truck from a couple months ago in Green Bay, is it?

And are you busy tonight? I was thinking about swinging down for the shifter ****...I can PM/call you if you want. I just need to know the general area again.

JeepCoMJ

yep.

and yeah. call me, you have my #

sorry for side-tracking...

Gee oh Dee

Would a compression test help determine if the bearings are toasted?

If a header bolt was indeed loose it should be somewhat easy to figure out.

dukie564

^^ this. 5w30 is actually even better and helps with cold engine starting

JeepCoMJ

no. the bearings have a minimal amount to do with what your compression is and/or the shape of your cylinder and rings. of course, without bearings, you wouldn't have compression, because it wouldn't be rotating.


basically, drain the oil and inspect it.

JeepCoMJ

true. but lighter oil also gives more symptoms that more viscous oils cover up.

that's why I'm suggesting the PO put gear lube in. gear lube works really well to cover up engine knock. sucks when you're on the recieving end of that.

Gee oh Dee

Looking for metal shavings/chunks in the oil and possibly pan?

Berserker

Hi.
I have a '93 xj, 4.0 engine and I had the exact same problem. When I first got it, it had a little bit of lifter ticking, but nothing major. When I changed the oil, I used what I use in my full-size 1990 Dodge truck; 3 quarts 10-w30 and 2 quarts 20-w50 (I know it sounds wierd, but hey, the truck is 20+ years old and the engine still runs strong with no oil burning, so I must've been doing something right.)
Anyway, I did the same thing to my xj and the engine started sounding like a diesel and got so bad, even my buddy, an ASE master mechanic, was convinced I had a serious rod knock. After agonizing over needing a new engine, I came across a post that suggested just using the called for 10-w30 oil. I changed the oil to the 10-w30 and believe it or not, all the scary noises gradually went away (took about 3 weeks). That was 2 years ago,and it still runs quiet. Hope this helps.