Knocking when cold
Thread Starter
Racer
Joined: Jul 2001
Posts: 265
Likes: 0
From: Levelland, TX USA
Knocking when cold
I bought a 2000 coupe a couple of weeks ago. It's got 15k miles and is still under factory warranty a bit longer.
The other morning i started it up-it was pretty cold outside. It started making a loud knocking/clacking noise. It stopped after a few minutes of warming up, but it concerned me. Weird thing is, this morning i fired it up cold, and it was totally quiet. I would think if a part were broken or worn, that it would occur every time.
I am thinking maybe valve train, lifter collapse, or something like that. Is it feasible that a lifter might give this intermitent problem? Has anyone experienced something like this? What was the end result? Did warranty cover it?
The other morning i started it up-it was pretty cold outside. It started making a loud knocking/clacking noise. It stopped after a few minutes of warming up, but it concerned me. Weird thing is, this morning i fired it up cold, and it was totally quiet. I would think if a part were broken or worn, that it would occur every time.
I am thinking maybe valve train, lifter collapse, or something like that. Is it feasible that a lifter might give this intermitent problem? Has anyone experienced something like this? What was the end result? Did warranty cover it?
Burning Brakes
Joined: Nov 2001
Posts: 783
Likes: 0
From: Statesboro Ga
Re: Knocking when cold (Darrell G)
Well, I had a little tapping noise in the valve train. I asked someone at work as well as posted the question. From how you describe your noise, it sounded like you had a louder knocking, but from the fact that it went away, it may not be a big deal.
The responses I got were basically that the oil may not have circulated thru the engine totally at first, so wait until it warms up, and that the tapping is a LS1 characteristic to some point. The funny thing about the noise is that I never noticed it until the weather started getting colder, so I figure that may have something to do with it, too.
But, when in doubt, get someone who really knows Vettes to listen to it. While I would like to get around to doing this just for sanity's sake, the noise is intermittent and does seem to go away when warmed up. Sorry if this isn't as technical of a response as you were hoping for, but it may provide some calm to your concerns. :seeya
The responses I got were basically that the oil may not have circulated thru the engine totally at first, so wait until it warms up, and that the tapping is a LS1 characteristic to some point. The funny thing about the noise is that I never noticed it until the weather started getting colder, so I figure that may have something to do with it, too.
But, when in doubt, get someone who really knows Vettes to listen to it. While I would like to get around to doing this just for sanity's sake, the noise is intermittent and does seem to go away when warmed up. Sorry if this isn't as technical of a response as you were hoping for, but it may provide some calm to your concerns. :seeya
Team Owner
Joined: Jul 2001
Posts: 21,374
Likes: 1,003
From: Various places in Southern California.
Re: Knocking when cold (Darrell G)
Sounds like piston slap, a fairly common problem with the LS1, especially at cold startup in very cold weather. Late in the 2001 model year they changed the piston (added a coating) that has reduced this problem.
According to most sources, including GM, this is not a problem, other than the fact a knocking engine sounds pretty crappy. Still, since you're still under waranty, I'd have a dealer look at it so you have the issue documented in case something goes bad later.
According to most sources, including GM, this is not a problem, other than the fact a knocking engine sounds pretty crappy. Still, since you're still under waranty, I'd have a dealer look at it so you have the issue documented in case something goes bad later.
Thread Starter
Racer
Joined: Jul 2001
Posts: 265
Likes: 0
From: Levelland, TX USA
Re: Knocking when cold (Darrell G)
Wouldn't piston slap be more consistant, knock everytime when started cold? My experience with piston slap in the old days was if it was piston slap, you could hear it every time when cold.
Melting Slicks
Joined: May 2001
Posts: 2,596
Likes: 120
From: East Tennessee
Re: Knocking when cold (Darrell G)
If its the 'usual' LS1 piston slap it will do it cold everytime (depending on the temp of course) - it just sounds like a forged piston(s) noise for a few minutes. Sometimes a lifter will bleed down and may be slow to pump up, I wouldnt worry unless it starts doing it often - may want to make sure your pressure is coming right up at startup. The older cars had oil pump problems due to a sticking relief valve but they have it pretty well fixed after 2001 from what I understand.
[Modified by kp, 1:59 PM 1/8/2003]
[Modified by kp, 1:59 PM 1/8/2003]
Melting Slicks
Joined: Mar 2002
Posts: 2,931
Likes: 2
From: Tx
Re: Knocking when cold (kp)
It could have just been caused be a carbon deposit. Sometimes these get reduced after some spirited driving and the noise goes away. You (or the dealer) could do a decarbonization procedure on it and see what happens. It's probably worth doing it once a year anyway.
Le Mans Master
Joined: Aug 1999
Posts: 5,411
Likes: 2
From: N Carolina 08 Z51 Coupe
Re: Knocking when cold (Scissors)
Piston slap.. also a lifter might not have been pumped up for that bit of extra noise. As long as it went away at normal temps... you are probably fine.
These engines are tough... just drive it slow until the oil temp hits 150.
Enjoy the car :steering:
Mike
These engines are tough... just drive it slow until the oil temp hits 150.
Enjoy the car :steering:
Mike
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Le Mans Master
Joined: Mar 2002
Posts: 7,692
Likes: 0
Re: Knocking when cold (C5~Missle)
mine worried me the same way...matter of fact after getting it, i was scared to drive it one morning because of this....all hs been fine....agreed..50k car shouldnt do this, but they shouldnt burn oil either
Le Mans Master
Joined: Jul 2000
Posts: 5,925
Likes: 0
From: A FEW CLICKS NORTH OF THE CANAL
Re: Knocking when cold (Duck916)
Sounds like piston slap, a fairly common problem with the LS1, especially at cold startup in very cold weather. Late in the 2001 model year they changed the piston (added a coating) that has reduced this problem.
According to most sources, including GM, this is not a problem, other than the fact a knocking engine sounds pretty crappy. Still, since you're still under waranty, I'd have a dealer look at it so you have the issue documented in case something goes bad later.
According to most sources, including GM, this is not a problem, other than the fact a knocking engine sounds pretty crappy. Still, since you're still under waranty, I'd have a dealer look at it so you have the issue documented in case something goes bad later.
This is all you can do short of having the dealer replace the pistons :nono:
Just make sure the oil temp is above 150 deg before driving.
Burning Brakes
Joined: Jan 2002
Posts: 1,147
Likes: 1
From: Geismar LA
Re: Knocking when cold (Darrell G)
My 02 has a different sound on cold startup, almost like a diesel sound. That doesn't concern me as it goes away on warmup. I've had several cars, actually with low miles, that have experienced a loud knocking at startup, almost like a rod knocking, but was probably a lifter stuck or colasped. I was told by the dealers to change the oil. That always seemed to help. Also, for winter driving, I recommend to use the 5W30, as its thinner cold and might help your knocking problem. Good luck.
Instructor
Joined: Jan 2002
Posts: 183
Likes: 0
From: Raleigh NC
Re: Knocking when cold (Darrell G)
Same issue on my 95 C4 when I had it. I knew it was a piston. GM said it was the flywheel. I insisted that it was internal to the motor. (Some power loss.) Knock would be gone-to faint- after reaching driving temps. They replaced flywheel and said, "Come pick it up.. It's completed! Best news... no more knock!" Went and picked it up... KNOCK KNOCK KNOCK. New short block for me....
It may be a toasted piston.... Insist on a tear-down. Get it done right.
It may be a toasted piston.... Insist on a tear-down. Get it done right.
