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btrentham

5.3 carbon knock

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I've seen this discussion before, but I saw that most 5.3L owners are not experiencing the knocking (supposedly caused by piston - slap or carbon buildup), however I am.  I have a 2001 silverado 5.3L ext cab Z71 with 20K.  It knocks for about a minute or so when I first start it, then you can't hear it anymore.  I first noticed this around 8K miles.  

 

I have heard that replacing the pistions is the only permanent fix.  I have also heard that replacing the pistons doesn't even fix it.  Is the best option just using some top engine cleaner every so often?

 

Any new info on this topic would be appreciated!

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I've heard that the top engine cleaner isn't a permanent fix, and it will mean you'll have to change your engine oil when done.

 

My observation has been that the guys that run these motors hard (alot of towing and hauling) seem to have less problem with the "start-up knock".  I wonder if it's just a coincidence, or if that means something...  ???

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btrentham,

 

BTW, welcome to the forum and site!  Here's my 2 cents on this, and what I remember from various discussions.  

 

Seems to be 2 varieties:  1) classic cold-start piston knock;

2) various intermittent "tickings" or "tappings".  Some have one, but not the other, some have both.  Listened to father-in-law's '00 6.0L this past weekend, and his cold start knock definitely sounds like it's coming from lower down in the engine, than, say lifter noise or upper engine carbon build-up noises.  

 

My '99 5.3L has intermittent very mild "ticking", and seems more prevalent after a lot of stop and start driving and short trips.  Like Shaners said in previous post, if the engine is driven a little harder, seems to quiet down the ticking.  I also noticed that after using Techron, the ticking has stopped.  These would lead me to believe that the "ticking/tapping" may be carbon build-up, rather than piston slap.  I'd like to get father-in-law to stand on the 6.0L sometime on a fairly regular basis to see if this helps - honestly, if it is piston slap, then I doubt hard driving would make any significant difference.

 

GM has been besieged w/ ticking and slap problems, mostly from 5.3 and 6.0 L engines, but my understanding is that deep-skirt block designs are more prone to this, maybe as it's harder to get a perfect alignment w/ piston and block skirt?

In the news section here on this site, there is discussion of a new all-aluminum 5.3L that will be used in the new SSR and also the "stretched" versions of the Envoy and Trailblazer.  The press releases go into some detail about polymer-coated pistons, so perhaps we will see this cascade to all LS1 engines in the future - here's to hoping.   :D

 

Despite what all the hollering sounds like, I think the piston slap issue is confined to a small percentage of LS1 engines.  If and when GM decides it's caused enough publicity, they will likely fix the issue.  Just hope this includes all older LS1 engines w/ slapping noises.  If you check out other topics, there are some threads related to piston slap and various noises as well.

 

Hope this helps.

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the last 4 days my truck has not had the knock on startup?  very strange...

 

i wonder if its the new $1.30 a gallon gas or maybe GM sent a team to my house saturday night when i was sleeping & they secretly performed some work on my truck... :ehh:

 

in any case i have not heard it... I even had my wife start the truck the am & i stood next to the frt passenger side & nada..  would be nice if it stays away

 

Truck just turned 32000 sat night before i parked it.. but from about 18-32K the knock was there....

 

Strange very strange :D

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My 2001 6.0 knocks less or very little since the outside temperature has been warmer at night. But I'm sure when winter comes, it will still do it.

:D

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:D   well its back.. today the knock was back... strange as its about the warmest am we have had... oh well

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Mine is the same way - the warmer it is the longer it knocks (or taps or whatever), but it quits in a few seconds to a minute. It's going to the dealer tomorrow, along with a tape I made of the noise. I'm running 93 octane gas in it and it seems to make it worse. I'll go back to 87 next time and see what happens. It has me more worried than it probably should but after how much these things cost, I expect it to not have any problems like this. Mine sounds like it is coming from the top of the engine. What happens is this:

 

On a cold start, it will tick for about a minute. If you give it the gas hard, it will stop ticking while the engine accelerates, but on the decelleration (no throttle) it still ticks. If it were a bleeding lifter, wouldn't it stop when I revved it (due to the increased oil pressure) and stay stopped? If it were a bad piston (such as piston slap), wouldn't it keep on knocking? Once it stops, it  doesn't come back until the truck has sat for about four hours or so. My old Lumina had a constant "tick" but it wasn't nearly this noticable.

 

This whole thing has me seriously considering an extended warranty! Anyone know about how much they are for about 100,000 miles?

 

It it does "blow up" it will be the last chevrolet I ever buy. I know ford isn't much good either so I guess I'll have to get a Dodge (scary thought - don't like them either). A friend of mine has a Toyota that does something similar. He had a problem with the dealer at first, and I don't know how it came out.

 

Another question - could this be a normal noise in most cars but more audible due to the plastic intake manifold (yes, they are plastic now)?

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Had the truck in the other day to get the new yoke put on.  I had some time to talk to the tech.  I asked if the Top Engine Cleaner was beneficial as a routine thing and he indicated that it wasn't really necessary unless you have symptoms.  I have no knock.  He said that a good fuel system cleaner, such as Techron, should prevent problems if used about every 3 or 4 tanks.

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My 02 with a 5.3 always has had this knock, I pull a race trailer with it alot and run it hard. I noticed on my last oil change, it seemes to knock worse, louder and longer. I always use a NAPA Gold oil filter, but this change, I did not make it to NAPA, and used a Fram filter. The filter was shorter, but it fit and did not leak. Wondering if this smaller Fram filter did not have the check valve, causing the knocking to be worse? Has anyone else ever noticed this?

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Changed oil and filter today used the NAPA Gold oil filter, knocking is very light, and does not last but 10 seconds. Whats going on with this?

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my truck will chatter if i start it in the cold...or if i run it on for awhile and let it sit and start it back up while still warm..vortecs tick, but its sure better then the newer modulars on fords, those things sound like their coming apart inside...btw i have 113k on the ticker and has knocked since i got it, 3k oil changes top end cleaned often with BG products...gm fuel system cleaner ran every 6k

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