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1991 Eldorado (Gone) ; 2001 Seville SLS (RIP) ; 2005 DeVille
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Discussion Starter #1 (Edited)
My engine recently started to knock.

The car ran just fine until it seems cold weather has arrrived. It does lighten up a little as time goes on, but still stays with me even after the engine has been fully warmed up. I have read up on cleaning with the GM TEC stuff to solve a "cold knock" but I don't think that will apply because it is always there, cold or hot. It does change with throttle. Much worse under hard acceleration. During a slow acceleration it is hardly noticable. Any ideas?

:banghead:

Dustin
 

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1991 Eldorado (Gone) ; 2001 Seville SLS (RIP) ; 2005 DeVille
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228 Posts
Discussion Starter #3
Ranger said:
Have you tried some good ole WOT?

Yeah, I have. On several occations. Took it on the highway and rode it hard in 2nd gear. Didn't really seem to help anything.
 

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1999 White Diamond ETC
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2,538 Posts
knocking, ticking, or pinging?

Knocking is not good, obviously. Get a stethoscope for cars (~$10) and with the engine on, try to find it if is coming from the lower end (ramps) or from above (Camshaft). Usually the ticking from the top is normal. You don't hear it while driving with the windows up, do you?
 

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2006 STS V8 AWD, '95 Ford Ranger
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28,963 Posts
If the car is running with the hood up and you are standing there when some one gooses the engine, do you jump back to get away from the flying parts or does it sound like the works are politely conversing with each other? A rod knock will be a very sharp rap that gets much worse with RPM and will really sound off on the over run. It will be obvious that something is trying to break. Most other noises that get gradually louder with RPM and don't change on the over run are probably valve related. The use of a stethoscope as suggested earlier is a very good idea.
 

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1991 Eldorado (Gone) ; 2001 Seville SLS (RIP) ; 2005 DeVille
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228 Posts
Discussion Starter #6
The ticking noise, I imagine from the injectors, is only really noticable with the engine cover off.

The engine sound just fine when idling and when be revved up. The knocking seems to come into play under load. Also, the knocking has seem to let up some in the past few days. I will see if I can borrow one of the stethoscopes from work and try to locate it.
 

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1991 Eldorado (Gone) ; 2001 Seville SLS (RIP) ; 2005 DeVille
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228 Posts
Discussion Starter #9
auroradude said:
Screw additives, ever tried using Premium Fuel? I always run 93.

Screw additives? Blind ignorance is too common these days, almost disgusting. Grow a brain before you post. Also, any response to my comment will be ignored, being as I'm sure I will get one, and I don't wish to start a battle.

Now, are most additives junk, I'm sure most would agree yes.

Are all additives junk? No.

Not to mention, where did that come from? I don't see any mention of additives on this thread. Along with the fact 93 Octane is a waste of money on my year car. The engine is tuned for regular gas. Only benefit of high grade fuel may be detergents.

Honestly...How would high octane fuel help anything in this thread? Our engines are not detonating or pinging.
 

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Cadillac Owners Connoisseur
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1,164 Posts
Trench said:
My engine recently started to knock.

The car ran just fine until it seems cold weather has arrrived. It does lighten up a little as time goes on, but still stays with me even after the engine has been fully warmed up. I have read up on cleaning with the GM TEC stuff to solve a "cold knock" but I don't think that will apply because it is always there, cold or hot. It does change with throttle. Much worse under hard acceleration. During a slow acceleration it is hardly noticable. Any ideas?

:banghead:

Dustin
Hey Dustin - I have noticed a sound before on my car that might be what you're describing. It sounds almost like there's a tiny diesel engine inside your Northstar. On my car at least, it goes away when the engine heats up. I've also tried lots of WOT (still do it just to be sure) and it never goes away. After much discussion with a guru who used to frequent this forum, I've chalked it up to normal valvetrain clatter. He had suggested using Rotella 15W-40 motor oil for one change cycle to see if the slightly heavier oil would quiet the clatter. I would only do that during the summer months, but I have never tried it. I'm convinced it's nothing to worry about, at least the sound I'm hearing from the front of my car when it's cold. Does yours sound kind of like a quiet diesel sound?
 

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mines has a uiet knock but only noticiable outside of car i was gonna try some slick 50 for heat and friction.....? wat u think the northstar engine does get really hot
 

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61 ragtop,2 67 eldos,68 ragtop,68CDV,93 ETC
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75 Posts
My 93 Eldo had a light knock when I first got it and I put a half can of sea foam in the oil and put the other half can down the intake then let the car sit shut down for 5 minutes and started it up and drove it till it quit smoking and the sound went away.It still has a cam/valvetrain tick but that sound has never changed and I think its normal. I know some additives are bogus but sea foam has worked for me many times and I use it in anything I have with an engine FWIW:xsmile:
 

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White Diamond '03 DHS (with DTS floor shift)
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keep it fresh said:
mines has a uiet knock but only noticiable outside of car i was gonna try some slick 50 for heat and friction.....? wat u think the northstar engine does get really hot
Save your money for something useful. Slick50 is snake oil.
 

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1999 STS - diamond white
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5,229 Posts
How many miles on it? I can't hear it obviously, but the symptoms point to rod bearings. Loads put a strain on the crank, heat and expansion diminish the sound by reducing clearance but it won't go away. I've heard that Rotella helps some.

That's my $.02. I hope I'm wrong.
 

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keep it fresh said:
mines has a uiet knock but only noticiable outside of car i was gonna try some slick 50 for heat and friction.....? wat u think the northstar engine does get really hot
Slick 50 is useless. It won't help friction or temperature. It only helps the finances of the Slick 50 company, not your car.
 

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1991 Eldorado (Gone) ; 2001 Seville SLS (RIP) ; 2005 DeVille
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Discussion Starter #16
mcowden said:
Hey Dustin - I have noticed a sound before on my car that might be what you're describing. It sounds almost like there's a tiny diesel engine inside your Northstar. On my car at least, it goes away when the engine heats up. I've also tried lots of WOT (still do it just to be sure) and it never goes away. After much discussion with a guru who used to frequent this forum, I've chalked it up to normal valvetrain clatter. He had suggested using Rotella 15W-40 motor oil for one change cycle to see if the slightly heavier oil would quiet the clatter. I would only do that during the summer months, but I have never tried it. I'm convinced it's nothing to worry about, at least the sound I'm hearing from the front of my car when it's cold. Does yours sound kind of like a quiet diesel sound?

That sounds pretty much like my problem. Only it can get pretty bad and only lightens up when warm.

Well, it really started to worry me so I bit the bullet and took it to the dealer. They said the noise is caused by sticky piston rings allowing the piston to wobble around somewhat. They said they have never seen any engine damage to to this. In order to fix it and prevent it from occuring again, It involves redesigned pistons and over $3000 in labor.

Sometimes a decarbonization will help, but I will do that myself sometime soon.

They didn't charge me anything, though. So that was a plus.


mcowden said:
Slick 50 is useless. It won't help friction or temperature. It only helps the finances of the Slick 50 company, not your car.
From what I understand that is the perfect truth, nothing more. If anything, it helps for only a few days. But seadfoam and the likes are awesome.
 

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The sound you are describing is either cold carbon rap, or piston slap. If you did the Seafoam or GM Top Engine Cleaner service and the noise is still there, it is most likely Piston Slap.

Although Piston Slap is not as prevalent in the Northstar as it is in the LS1, there are more than a few documented cases in Northstars. When the dealer told you about "the piston wobbling around a little bit", he was describing the cause of piston slap. Basically the clearance between the piston diameter and cylinder bore is a little more than it should be, and this allows the piston, which has a relatively short skirt, to rock slightly, causing the noise you are hearing. As the engine warms up, this clearance decreases and the noise will generally disappear, or at least become almost inaudible. Most Chevy dealers will give you an extended engine warranty (up to 8 years / 100,000 miles) if they choose not to tear into the LS1 engine. I have not heard of any Caddy dealers willing to do anything about this in Northstars unless the customer is willing to pay.

To learn more about the GM Piston Slap issues go to:
www.pistonslap.com
 

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1991 Eldorado (Gone) ; 2001 Seville SLS (RIP) ; 2005 DeVille
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Discussion Starter #18
I did try the Top engine cleaner. What you said seems to pretty much be what I have. unforutnatly.
 

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Trench said:
I did try the Top engine cleaner. What you said seems to pretty much be what I have. unforutnatly.
I have noticed the same thing on my car. It hasn't changed in 62,xxx miles, so I'm not worried about it. I give it lots of WOT and have also done the TEC stuff and it makes no difference. The sound is so quiet, though, I don't always notice it and when I do, I just ignore it. Obviously it's not getting worse and the engine runs fine so I don't worry.
 

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1991 Eldorado (Gone) ; 2001 Seville SLS (RIP) ; 2005 DeVille
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Discussion Starter #20
mcowden said:
I have noticed the same thing on my car. It hasn't changed in 62,xxx miles, so I'm not worried about it. I give it lots of WOT and have also done the TEC stuff and it makes no difference. The sound is so quiet, though, I don't always notice it and when I do, I just ignore it. Obviously it's not getting worse and the engine runs fine so I don't worry.

Mine can sound aweful as all hell when cold. Usually it lightens up when the engine warms up. Usually I can still hear it pretty well. Sometimes it seems to go away, though. It just sounds like crap.

Ain't I pimpin'
 
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