Hello, my Jeep's been making a knocking grinding noise since I got it at idle. Noise isn't there when above 1500rpm, cold start it starts great about 30-45 seconds in it starts making the noise. once you drive a little bit and let it idle hot the noise is very faint sometimes or not there either. All flexplate bolts are tight. I seafoamed the truck and tried some different weight oil , didn't do any good. Oil pressure is great. 2001 xj automatic. Any insite would be great. Here's a link for video. https://youtu.be/eAl3H8S4A0Y
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Flexplate or lifters ?!?
- Thread starter Don_ayy5
- Start date
A mechanics stethoscope is good for pin pointing noises down to a single part. Mine is a basic old one that has a long piece of vacuum hose for listening and I stick a bolt in the end when I want to touch parts for the noise.
https://www.amazon.com/Lisle-52500-Mechanics-Stethoscope/dp/B0002SQYSM
https://www.amazon.com/Lisle-52500-Mechanics-Stethoscope/dp/B0002SQYSM
I used a stethoscope there was some noise from the bell housing some from the oil pan and some from under the valve cover, it's really hard to say noise travels. It is not effecting driving at all or performance that I know of. Just wondering if anyone's had his problem and what it is. Saw a couple videos on YouTube and one guy said his jeep made that noise for 140k miles and nothing ever happened. Now that's great and I'll drive it till it blows but.... I kind of want a explanation haha
Ronbo
NAXJA Forum User
- Location
- San Marcos, CA
Were you able to inspect the flexplate for cracks?
old_man
NAXJA Forum User
- Location
- Loveland, Colorado
That sounds loud enough to be rod bearings or a collapsed lifter. I would pull the valve cover and listen at each lifter hole.
When you say the flex plate bolts are tight, did you check the ones to the crank?
When you say the flex plate bolts are tight, did you check the ones to the crank?
I couldn't see any visible cracks. But it could be possible behind it against the torque converter. I was thinking collapsed lifters but the truck starts easy I would think it would start hard bc the valves wouldn't be moving. And if bearings it would go with Rpms and not go away above 1500rpm right ? And after driving and let it idle hot it barely makes the noise if it's even there at all.
old_man
NAXJA Forum User
- Location
- Loveland, Colorado
A collapsed lifter still moves the valve, it just doesn't move it as much and makes a nasty racket. Either way you really need to fix this before you drive much more or you may end up with a trashed engine.
With the amount of noise you are getting, I would definitely pull the valve cover and see/hear what is going on. If it is the flex plate, you won't hear much if any change.
With the amount of noise you are getting, I would definitely pull the valve cover and see/hear what is going on. If it is the flex plate, you won't hear much if any change.
Last edited:
- Location
- MilkyWay Galaxy
That is sticking lifters, I know that noise all too well on the 4.0, LOL. It is also not a real serious problem.
I have found, thanks to a trick 5-90 taught me, that if you run the engine at 3500-4000 rpm once warmed up for 120 to 10 seconds, respectively, the noise goes away at all speeds. May come back on cold start ups, but clears up by repeating the process. Adding some MMO to the oil helps some too.
I have found, thanks to a trick 5-90 taught me, that if you run the engine at 3500-4000 rpm once warmed up for 120 to 10 seconds, respectively, the noise goes away at all speeds. May come back on cold start ups, but clears up by repeating the process. Adding some MMO to the oil helps some too.
- Location
- MilkyWay Galaxy
That is not a cracked flex plate noise.
- Location
- MilkyWay Galaxy
It is caused by the lifters sticking (varnish) that stops them from rotating, according to 5-90. I have had that problem for 70,000 miles and 12 years on my 290,000 mile 87 Wagoneer XJ. It is almost 100% gone, 100% of the time now, now that I learned and used the 3500-4000 rpm trick in park and fixed other issues like fuel running too rich, and a better spark plug choice......etc.
- Location
- MilkyWay Galaxy
Yeah. It depends on the day it gets better and worse and if I thought it was something catastrophic I think it would be a lot worse while driving. I Deff will check the lifters, but if It blows I was going to do a reman engine anyways
Sticking noisy lifters on the 4.0 are common and many others drive them noisy with no problem. Mine got so noisy one cold day it sounded like the engine would grenade. That was 8 years and 40,000 miles ago.
Your sound bite was mild in my experience. If it got say 4-5 times louder and did not go away as you say at 1500 rpm, I might worry and pull the head and replace parts as needed.
I am going pull the head on mine, finally, this year and service them only because two of my exhaust valve guides have massive side play in them and suck oil like crazy. I have to clean the spark lugs about every 500 miles on two cylinders with the bad valve guides.
Runnin'OnEmpty
NAXJA Forum User
- Location
- Southeast USA
I agree with the sticking lifters diagnosis. Even though you've Seafoamed and tried an oil change, as stated a can of Marvel Mystery Oil might help. Running a synthetic oil for a change interval might also help.
The fact that the noise gets quieter after it warms up is classic for sticky lifters....
moparmansfield
NAXJA Forum User
- Location
- Portland
I've had 3 xjs(one current dd) and 1 mj that did this. Haven't tried that high rpm trick. Will try it and report back.
Thanks for the advice! The noise is rather emberessing and would like to fix it. With theMMO do you take a quart of oil out and add it and run it till the next oil change? Or is it like the seafoam? And also you said run it 4000rpm for 120-10 seconds ? Not really sure I understand that correctly lol, how would that clear or sticky lifters ?
Should I try running a quart of marvel mystery oil for 3000miles and see if it helps ? I tried some lucas oil but hasn't seemed to work maybe made it worse bc maybe it's not a weak lifter that's draining but a sticky one?
- Location
- MilkyWay Galaxy
Yes, swap one quart of MMO for the full 3000 miles. I would not risk synthetic oil and it is costly. It can over clean too fast, make it worse, and cause rear main and other seals to leak like mad on older rigs that have miles on them using dyno-oil. When mine is noisy I tell them it is a diesel LOL.
120 seconds at 3500 rpm, or 10-20 seconds at 4000 rpm. I used 3500 for a year first, as I was afraid to push the engine and noise any higher at first. As the noise cleared up I was able to take her to 4500 rpm for 30 seconds with no issues. Start at the low end, 3500 for now.
120 seconds at 3500 rpm, or 10-20 seconds at 4000 rpm. I used 3500 for a year first, as I was afraid to push the engine and noise any higher at first. As the noise cleared up I was able to take her to 4500 rpm for 30 seconds with no issues. Start at the low end, 3500 for now.
- Location
- MilkyWay Galaxy
Right, Lucas does not help the sticking lifters. I use it on mine to slow the oil consumption in the summer...not to clean and quite the lifters.
- Location
- MilkyWay Galaxy
It forces the sticking lifters to rotate again, thus unsticking them per 5-90-Naxja in old chats here.
Okay awesome, how long should it take for the marvel to work and notice some sort of difference? I'm sure every jeep is different but you know better then I do as you've used it before
