Chuck
Cold start engine rap - does anything help?
Tech Contributor
Joined: Oct 1999
Posts: 41,058
Likes: 9,820
From: Charlotte, NC (formerly Endicott, NY)
Never heard it isolated to a specific cylinder before. A little difficult to attribute to one cylinder as they are all assembled to the same tolerances. Who put a stethoscope on that cylinder and listened to see if it was the one making the noise?
Bill
Bill
Le Mans Master
Joined: Oct 2004
Posts: 5,841
Likes: 19
From: CLT, North Carolina
It would be interesting to take a survey among GM service techs who have played a role in LS series piston noise over the years to see if service history supports certain cylinders are more often the culprits. I suspect it is probably random and that the likely cause is tolerance variation stack-up with bore size on the large limit matched with pistons on the small side of the diameter tolerance range.
Easy fix though if you get tired of hearing the racket... Some Saturday when you don't have anything better to do just zip all 8 pistons out and measure and replace as necessary. You'll need a good accurate dial bore gauge with tenths resolution and a good outside mike. Measure a piston, "zero" the dial bore gauge and check its mating cylinder to find out what the running clearance was. You'll have your answer and this is the only way you will be able to get rid of the piston noise (which is actually doing no harm).
There will be absolutely no adverse effects for the life of your engine should you just decide to live with it and do nothing.
Easy fix though if you get tired of hearing the racket... Some Saturday when you don't have anything better to do just zip all 8 pistons out and measure and replace as necessary. You'll need a good accurate dial bore gauge with tenths resolution and a good outside mike. Measure a piston, "zero" the dial bore gauge and check its mating cylinder to find out what the running clearance was. You'll have your answer and this is the only way you will be able to get rid of the piston noise (which is actually doing no harm).
There will be absolutely no adverse effects for the life of your engine should you just decide to live with it and do nothing.
Racer
Joined: Nov 2008
Posts: 378
Likes: 0
My 1999 doesn't have it. My 2002 LS1 did. It seems to be 2001-2004 LS1's that are most prone to having it. Not all LS1's have this problem.
Pro
Joined: Sep 2005
Posts: 693
Likes: 0
From: Gilbert AZ
It's normal, it won't get worse with mileage and will not affect performance. The vast majority of 2001-2004 LS1's have this. GM calls it "cold start noise", for the rest of us in the real world it is piston slap coming from #7.
The only harm this causes is starting your car in front of people when it's cold and knowing they hear it!!! There are no additives etc. to stop or even quiet it down. Enjoy your car, the noise is normal.
The only harm this causes is starting your car in front of people when it's cold and knowing they hear it!!! There are no additives etc. to stop or even quiet it down. Enjoy your car, the noise is normal.
Perfectly normal. 
Burning Brakes
Joined: Jan 2000
Posts: 1,226
Likes: 80
From: Ohio
I have it also but just for 15 to 30 seconds after start-up. And then only if I let the car sit for a while after start-up instead of driving away immediately. I use standard Delco filter this seems to work best for this problem. 
Racer
Joined: Nov 2008
Posts: 378
Likes: 0
Yes, myself and other LS1 owners at Thompson Raceway Park (used to live in Ohio) all had this noise in #7 only.
Tech Contributor
Joined: May 2008
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From: Somers, CT and Clermont, FL
St. Jude Donor '09-'10-'11-'12-'13-'14-'15-'16
My first thought was they were just feeding you some
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Thread Starter
Drifting
Joined: Nov 2007
Posts: 1,616
Likes: 11
From: Newport, RI
..... engineer whom explained it to me. He said the "cold start noise" is in cylinder#7, common in most LS1 engines and was nothing to worry about. I don't know, I'm sure it can be in other cylinders as well, but the way he explained it, was a flaw in the production line which caused this in #7.
Yes, myself and other LS1 owners at Thompson Raceway Park (used to live in Ohio) all had this noise in #7 only.
Yes, myself and other LS1 owners at Thompson Raceway Park (used to live in Ohio) all had this noise in #7 only.
Damn, that's interesting. I wonder if I could test mine by simply disconnecting the plug wire. If I kill the spark to #7, then that should stop the slap, right?
-
Race Director
Joined: Jul 2007
Posts: 11,467
Likes: 8
From: 972 and 405
Tech Contributor
Joined: May 2008
Posts: 3,100
Likes: 17
From: Somers, CT and Clermont, FL
St. Jude Donor '09-'10-'11-'12-'13-'14-'15-'16
Burning Brakes
Joined: Oct 2007
Posts: 790
Likes: 0
From: Sebastian Sunshine
slick50 or dura lube
Just bought a 2004 C5 coupe with auto and 15K miles. It has a very noticeable rapping when cold. I probably shouldn't have bought the car, but I test drove it when warm and there was no rapping. The engine really has to warm up before the rapping goes away. I'm disappointed the seller never mentioned this.
I'm assuming it's a piston which is a loose fit to its' bore, and I know there are issues about GM piston fitment. I also realize that alum pistons expand/contract at different rates than steel blocks. I've owned plenty of other Chevy cars which made the cold engine noise, but this one seems kinda bad.
Are you guys using any special oils or additives which reduces this rapping?
thanks
I'm assuming it's a piston which is a loose fit to its' bore, and I know there are issues about GM piston fitment. I also realize that alum pistons expand/contract at different rates than steel blocks. I've owned plenty of other Chevy cars which made the cold engine noise, but this one seems kinda bad.
Are you guys using any special oils or additives which reduces this rapping?
thanks
Tech Contributor
Joined: May 2008
Posts: 3,100
Likes: 17
From: Somers, CT and Clermont, FL
St. Jude Donor '09-'10-'11-'12-'13-'14-'15-'16
Race Director
Joined: Jul 2007
Posts: 11,467
Likes: 8
From: 972 and 405
-Alex
Racer
Joined: Nov 2008
Posts: 378
Likes: 0
IMO, it makes more sense to have the slap attributed to only one specific cylinder otherwise, some cars would have it in all of them, or at the very least, 2 or 3. Could you imagine the noise? I'll see what more I can find out about this #7 theory that I've thrown out there. I also found an article on the internet about it, but that was 5 years ago.
I'll see what I can dig up, but in the meantime, has anybody actually heard this in more than just one cylinder?
I'll see what I can dig up, but in the meantime, has anybody actually heard this in more than just one cylinder?
Racer
Joined: Mar 2007
Posts: 299
Likes: 0
From: Bahrain
I have the exact same engine in my works car (Aussie built Caprice SS) which has always had the "noise" at cold startup.
After a couple of minutes at idle the noise goes away.
For what its worth she has just completed 300,000 miles with nothing but regular oil and filter changes.
These engines are tough!
After a couple of minutes at idle the noise goes away.
For what its worth she has just completed 300,000 miles with nothing but regular oil and filter changes.
These engines are tough!
Instructor
Joined: Aug 2008
Posts: 169
Likes: 0
From: Anchorage AK
From what i know (which may not mean much), oil delivery has nothing to do with this "problem". It's all in the design of the piston. In order to get the tolerance needed at warm operating temp, the piston is a little small when cold. Also, in order to lighten the piston, the skirt is made a little shorter. Combine these two, and you have a piston that can wiggle a little when cold and cause a knocking noise. Mine has always done it and it's never gotten louder and i thrash on mine. It goes away within 15-30 seconds of start up.
If you think the LS1 is bad, go listen to a Subaru when it's cold. My wife has a Subaru Outback. Jesus, those things sound like diesels when they're cold and some of them take many miles before they warm up enough for the sound to go away. It's so loud when it's cold, i swear you can feel the knock through the floor board when you're driving. I've had multiple mechanics, both Subaru trained dealer techs and privately owned repair shops, tell me it is normal.
If you think the LS1 is bad, go listen to a Subaru when it's cold. My wife has a Subaru Outback. Jesus, those things sound like diesels when they're cold and some of them take many miles before they warm up enough for the sound to go away. It's so loud when it's cold, i swear you can feel the knock through the floor board when you're driving. I've had multiple mechanics, both Subaru trained dealer techs and privately owned repair shops, tell me it is normal.
Safety Car
Joined: Oct 2000
Posts: 4,949
Likes: 10
From: Monticello MN
Out of curiosity, how does the sound that piston slap makes differ from lifter noise or a cold engine leak from an exhaust manifold seating surface. I have a noise on cold startup, for about a minute, or so, in the morning, that I thought was from a sticky lifter. Inquiring minds want to know how to tell the difference. 
Ed
Ed
Thread Starter
Drifting
Joined: Nov 2007
Posts: 1,616
Likes: 11
From: Newport, RI
Out of curiosity, how does the sound that piston slap makes differ from lifter noise or a cold engine leak from an exhaust manifold seating surface. I have a noise on cold startup, for about a minute, or so, in the morning, that I thought was from a sticky lifter. Inquiring minds want to know how to tell the difference.
Ed
Ed
- Lifter noise is usually a lighter clacking-type sound
- Exhaust man leak is usually a sharper noise, again fairly light
- Piston slap is heavier - engine will sound like a diesel
-
Burning Brakes
Joined: Aug 2006
Posts: 753
Likes: 2
From: Denville NJ
Oh come on now.
We are all relieved that their is no impending disaster awaiting us.
However the question is posed regarding the possible effect of oil additives. Someone out there must be dumping all kinds of "mystery oil" and "STP" etc. down the oil filler.
Spit it out please, does it help or not?
We are all relieved that their is no impending disaster awaiting us. However the question is posed regarding the possible effect of oil additives. Someone out there must be dumping all kinds of "mystery oil" and "STP" etc. down the oil filler.Spit it out please, does it help or not?