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Knock at start-up

This is a discussion on Knock at start-up within the General Help forums, part of the LSx Technical Help Section category; 00 ta 110k mi I recently switched to mobil1 5w30 synthetic and ever since i have had a knock or ...

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    Knock at start-up

    00 ta 110k mi I recently switched to mobil1 5w30 synthetic and ever since i have had a knock or rattle after cold start-up. I did not notice this before i changed the oil, but it was a bit warmer. It goes away once the rpms come up in first or second and don't come back till it sets for a long time and getd cold. Any ideas? Do they all do this? This is my first ls1, is this normal?

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    Member supercopone's Avatar
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    Sounds like it might be a little piston slap, GM says it norm, but I might be wrong I was reading something like this on another post. I would search "piston slap" or ur shit might be about to blow up..lol

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    Quote Originally Posted by croslod View Post
    00 ta 110k mi I recently switched to mobil1 5w30 synthetic and ever since i have had a knock or rattle after cold start-up. I did not notice this before i changed the oil, but it was a bit warmer. It goes away once the rpms come up in first or second and don't come back till it sets for a long time and getd cold. Any ideas? Do they all do this? This is my first ls1, is this normal?
    i dont know how long you've had this car, but it sounds like the common ls1 piston slap. it sounds like a knocking sound, and when you build a little heat in the motor it goes away. its an annoying sound but doesnt appear to cause harm. mine has 114k, and does it till i get to the first stop sign from my garage. i just bought an 02 corvette and it does it only not as loud. a co-worker bought an SS new in 02 and it did it. it seems more likely, or at least more noticeable as the air temp gets colder. some oils seem to quiet it but i wouldnt swear to it. at least you probably dont have to worry about an oil pressure or delivery problem.

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    Yeah baby! Yeah! silverWS6's Avatar
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    My 98 does the same thing, when i start her up it seriously sounds like the engine took a shit and it has no oil or like a rod knocking but after like 2 seconds it goes away and she runs fine. No loud noises or anything out of the ordinary and she has 195k. My 02 however doesnt do it but then again she barely turned 70k

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    Awaiting Activation jsremmos's Avatar
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    Dont worry about a thing... Its piston slap most likely... When I first got the mine it didnt do it but at about 19K it started the sound made me want to throw up. Ive gotten use to it. If you a do a search in the forum you will find a ton of posts. Hell one was from me a long time ago

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    Thanks, figured it was normal but thought i would check to see to be sure. It sounds like a damn duramax till i get out of the driveway in the morning or the parking lot after work, after it gets to about 2500 in second it just goes away.

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    Quote Originally Posted by jsremmos View Post
    Dont worry about a thing... Its piston slap most likely... When I first got the mine it didnt do it but at about 19K it started the sound made me want to throw up. Ive gotten use to it. If you a do a search in the forum you will find a ton of posts. Hell one was from me a long time ago
    hey were pretty close, ive never seen your car tho, im in tyler alot

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    GM....like a knock........

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    Moderator Cutlass's Avatar
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    Hmmm... I don't know guys. The piston slap I'm familiar with lasts about 30 seconds to a minute. This almost sounds like he's describing a lack of oil, rod knock type noise. The same noise that happens after an oil change before the filter fills up with oil.
    If thats the case then its not quite as normal or acceptable as piston slap.

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    Hope its not the rods,that would suck. How common is oil starvation in ls1's at start up and what would cause that? Also i didn't notice it as much before switching to mobil1 5w30 synthetic, but it was a lot warmer.

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    Quote Originally Posted by croslod View Post
    Hope its not the rods,that would suck. How common is oil starvation in ls1's at start up and what would cause that? Also i didn't notice it as much before switching to mobil1 5w30 synthetic, but it was a lot warmer.
    Did you change to a different kind of filter when you changed oil?

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    If it goes away when warm don't worry about it. My 5.3 Z-71 has done since I bought it and has 196k now and going strong...

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    Senior Member Redphoenix1998's Avatar
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    Also could be a lifter not pumping up. Common issue on cough cough Fords Cough cough but it happens

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    Quote Originally Posted by blackcar View Post
    Did you change to a different kind of filter when you changed oil?
    I don't remember what was on it before, it was the first time i changed since i purchased it. I used fram on everything my whole life till i read a post on here where sarge i think said they were junk,so i switched to ac delco filter

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    Member blackcar's Avatar
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    Quote Originally Posted by croslod View Post
    I don't remember what was on it before, it was the first time i changed since i purchased it. I used fram on everything my whole life till i read a post on here where sarge i think said they were junk,so i switched to ac delco filter
    Some filters will keep the oil from draining backwards through the filter (i.e. K&N and NAPA) some don't. If the filter that was on it before did and the AC Delco doesn't. That could be the prob. Not sure if AC delco does or not.

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    Member DaddySS's Avatar
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    I assume you don't know what kind of oil was in there either? Was it synthetic? The AC Delco filters are excellent so I wouldn't guess that was your problem. If it were me, I would switch to a good dyno oil - Castrol, Penzoil, etc. whatever your preference just as a test. You are right to avoid Fram filters, they are the worst. Piston slap does not need the RPMs to come in first or second, it goes away after 30 to 60 seconds. If you let your car idle for a few minutes does the noise go away or does it stay until you raise the RPM?

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    Senior Member redbird555's Avatar
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    Many peoples last more than 30-60 seconds atleast mine does its audible till operating temp then it goes away ie about 10 min. If you can rev the engine and the noise disappears you do not have a rod problem or a bent pushrod. Those will get louder as the rpms go up the rod especially will be REALLY loud. Try using a 10w40 dino oil i started using Pennzoil YB per advice from bobistheoilguy.com and it has significantly decreased the slap even over the german castrol.

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    Moderator Cutlass's Avatar
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    If it is an oil drain back problem, then maybe the oil pump pickup o-ring is torn/worn or the pick up isn't installed all the way or has a crack or pin hole in it. That could cause the oil pump to have to reprime itself after a cold start up.

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    Moderator Cutlass's Avatar
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    Quote Originally Posted by redbird555 View Post
    Many peoples last more than 30-60 seconds atleast mine does its audible till operating temp then it goes away ie about 10 min...
    Yeah now that I think about it, you're correct. I've had quite a few last longer then 1 minute.

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    Don't worry about it and drive the pi$$ outa that sucker once oil gets up to operating temp......

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