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Unread 08-04-2011, 09:16 PM   #1
04freedomgc
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Question Jeep knocks on startup, then goes away.

This is going to be a very long post.....sorry.....I have a 2004 Jeep Grand Cherokee Freedom edition (regular laredo with imo nice appearance package.) 4.0 auto trans. I have owned the Jeep for about a year. It currently has 93k on it, had 85k when I bought it. have changed oil roughly every 3000-3500 miles. Recently changed the oil with the usual 10w30 castrol gtx, put in the regular 6 quarts, but used a mopar filter (figured as with my toyotas the factory filter must be good). Everything was fine, drove to work and home, went to crank the next day, and heard a really bad knock (sounds like a rod knock).oil pressure slightly above middle.. turned the jeep off immediately. when starting the jeep again, it cranked for about 2-3 seconds then started, very slight tapping sound, but nowhere near what i heard at first (oil pressure still good). Drove the jeep and tapping slightly dissapears. Figured I had got a bad filter. Got Napa gold filter changed with 5 quarts of valvoline high mileage, and added a quart of Lucas HD oil stabilizer. cranked engine, recieved exact same knock, shut off immediately, cranked again, engine noise slightly there. Drove for about 15 mins, engine noise gone, runs great and great oil pressure......Figured I would go back to the normal oil filter, fram tough guard TG16. Still having exact problem. Jeep runs great after second start, but still knocks loud at startup until i shut off and crank again. when I crank again still takes 2-3 maybe 4 seconds to start, but when it does the very slight tapping sound almost dissapears. This sound is always towards the rear of the motor closest to the firewall. There is no noticeable vibrations in the shifter or on the motor when the hard knock is present. I am very stumped...going to check flexplate bolts, but this is nowhere close to what i have read on them. Worried i have a broken piston skirt or bad rod bearings......Also, dont think this has anything to do with it, but I do have a very very small rear main seal leak. If anyone has any ideas please let me know....very close to taking to stealership, or doing rings, rod bearings myself. This shouldnt be happening on a 93k engine. Sorry for the insanely long post, but want to give all info I can, hoping you guys can help. Thank you for reading.

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Unread 08-04-2011, 09:43 PM   #2
meopilite
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id guess lifters. pretty common with inline 6 cylinder engines. if it was a rod bearing, it wouldnt go away, it would get worse as you drive or the faster you drive.

inline 6 cyl. need an oil with a high zink content. most oils today have low zink. the lifters will eventially start ticking when deprived of zink. wal-mart brand oil (super-tech) has a good amount of zink in it. i would try the synthetic super-tech oil and see what happens.
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Unread 08-04-2011, 10:00 PM   #3
wsar10
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^^ this is posibly your "tap".

but wholy **** dont take his oil recomendation
http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=2070845&page=1

ST has lower zinc content than most any oil out there, this oil is plain crap for the 4.0.

If your looking for a good 4.0 oil go with Rotella T5 has well above 1000ppm of both zinc and phosphorus, also has a GREAT add pak with goodies like seal conditioners and a good detergent level...best part is it's only 16 bucks a gal. (here).

and get rid of that fram filter crap, go with a good old wix or better yet a puralator "PUREONE" the gold colored filter.
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QUOTE=billzcat1;wsar10 is right on point on this oil thread - as usual. Anyone reading this would be well-served taking his advice.


-03 WJ laredo 4.0 120k a few minor mods
-93 XJ 5spd, 3" zone lift
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Unread 08-04-2011, 10:11 PM   #4
04freedomgc
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Would the lifters be as loud as a rod knock? When I was much younger I bought a Honda CRX with a large hole in the block and black rod bearings that still slightly ran, eventually swapped the motor. this sounds as loud as that but without the hole . However, it gets very quiet and drives like normal after the second crank. I read a few threads about the lifters sticking, or leaking down over night, but didnt think thats what I had as it is very loud at start up.
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Unread 08-04-2011, 10:13 PM   #5
wsar10
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lifters would not be that loud, but very noticable.
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QUOTE=billzcat1;wsar10 is right on point on this oil thread - as usual. Anyone reading this would be well-served taking his advice.


-03 WJ laredo 4.0 120k a few minor mods
-93 XJ 5spd, 3" zone lift
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Unread 08-04-2011, 10:21 PM   #6
04freedomgc
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After thinking about it being the lifters that would make sense. If the lifter leaks down overnight, then the cam hits the lifters on a cold start before they are "pumped up", then the jeep cranks for a few seconds to build pressure to the lifter, then the sound goes away. I'm willing to try the Rotella T5....does it have different weights (10w30) like the reg oil? Should I put lucas in with the rotella? Also, how long would it take this sound to go away? It has to be damaging something right?
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Unread 08-04-2011, 11:25 PM   #7
shockracer
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Any chance it being piston slap?
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Unread 08-05-2011, 12:09 AM   #8
04freedomgc
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I am not too familiar with piston slap. tried to look a couple videos up on youtube, but nothing sounded similar....could be the audio quality too though.
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Unread 08-05-2011, 05:23 AM   #9
wsar10
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Quote:
Originally Posted by 04freedomgc View Post
After thinking about it being the lifters that would make sense. If the lifter leaks down overnight, then the cam hits the lifters on a cold start before they are "pumped up", then the jeep cranks for a few seconds to build pressure to the lifter, then the sound goes away. I'm willing to try the Rotella T5....does it have different weights (10w30) like the reg oil? Should I put lucas in with the rotella? Also, how long would it take this sound to go away? It has to be damaging something right?
you can get T5 in 10-30, 10-40.
But this is a HDEO so the 30w will be more like a light 40w,
and no LUCAS is worthless for anything other than increasing the viscosity of oil, mostly for high mileage engine where guys are trying to increase oil PSI, really LUCAS has nothing in it to benefit your engine.
You should never really have to add anything to your oil, if you need to than you need to go with a different oil that suites your needs.

If you wanted a heavier oil than go to Rotella T 15-40 but I would'nt in a low mileage engine like yours.

Don't get the wrong idea that T5 is a fix all, it will not "fix" your noise it may help it, but I'm recommending it simply because it is one of the best oils on the market for the 4.0.
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QUOTE=billzcat1;wsar10 is right on point on this oil thread - as usual. Anyone reading this would be well-served taking his advice.


-03 WJ laredo 4.0 120k a few minor mods
-93 XJ 5spd, 3" zone lift
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Unread 08-05-2011, 06:13 AM   #10
JeepNaked9969
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I had this same noise in my 06 I6 tj, and after reading on these wonderful forums, I decided to start cheap. So I tried some sea foam, which from my understanding is basically a high detergent oil. I put 1/3 in the TB and the rest in the crank case 2 days before my scheduled oil change, changed the oil and filter and put reg valvoline 10w30 in and it hasn't givin me trouble since.
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Unread 08-05-2011, 07:34 AM   #11
JForest2
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Reading what the OP has said, it's strange that the sound would be there right at startup, and then almost be totally gone after he shuts it off and restarts...

I doubt it's the lifters because it takes more than a couple of secs to prime them...

If it was a rod knock it sounds more like a dull thumping or a sharp dull tapping sound..

But I'm thinking it could be piston slap myself.. But then again it could be the lifters also.. Just thinking back to a car that we had in our garage and it had the same symptoms and it turned out to be the lifters..

If you want drop a quart of trans fluid in the oil or Marvel's Mystery Oil instead of one quart of oil.. Run it for about 50 miles get the motor nice a hot.. Maybe a highway run, and then change the oil and put in fresh oil..

Maybe you have a couple lifters that are sticking at start-up.. The trans fluid should unstick this..


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Unread 08-05-2011, 10:22 AM   #12
04freedomgc
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I will ditch the lucas, and try the rotella for the zink benefits, and go back to the Napa Gold filters (wix i believe) or the purolator gold per your recommendation. If I dont see any changes I am going to drop the oil pan to see if the skirt has been knocked off one of the pistons..have read a few threads that the motor will run great but have a knock like piston slap, and the skirt will be broken off of one side..after reading "knock knock" thread I am a little worried about that. Most say their knock is constant with the broken sleeve. However, I will keep this updated once I find the problem. Thank you all for your help. I really appreciate it.
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Unread 08-05-2011, 10:47 AM   #13
billzcat1
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I'm guessing cracked piston. It's far more common in 4.0s than the 4.0 fans would have you believe.
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Unread 08-05-2011, 10:55 AM   #14
MONSooNmonkey
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Use a little lucas in place of about 1CUP of oil, or half a quart. This'll quiet the knock on cold starts.

Lucas Motor oil additive
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Unread 08-06-2011, 11:33 AM   #15
meopilite
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Quote:
Originally Posted by billzcat1 View Post
I'm guessing cracked piston. It's far more common in 4.0s than the 4.0 fans would have you believe.
Since when is this common? Pistons only crack under abuse or if the timing is set pretty bad and ran for a long time like that.
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