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Q: Engine knocking on start up on 2000 Chevrolet Silverado 1500

My 5.3 V-8, with 120K miles, "knocks" a little on start up. After about a few minutes, it stops. Oil level is fine. Oil pump? Bearings?
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This is not likely to be a lifter. My 2000 with 5.3L does the same, and has for over a year (has 86K miles on it now). There is all kinds of info posted on the internet about it. Apparently there is a bore distortion or piston/cylinder clearance issue when the engine is cold (aggravated by the short pistons on the 5.3L), particularly after you get some miles on the engine, and what you're actually hearing is piston slap. The odd thing in my truck is that I hear it better in the cab than from outside. Don't know if that means it's on one or more of the rear cylinders, or just has to do with how the noise is transmitted through the structure. Annoying as hell, but short of a new engine there's not much that can be done. I think mine has gotten more noticeable in the last year - cold weather is the worst for it. GM naturally claims it will not be detrimental to engine life. I'm way out of warranty, so I'll drive her til she pukes one way or the other. Do an internet search on 2000 Silverado piston slap, you'll find a lot of people with similar experience. Apparently they did something in the '03 & newer models to get rid of this issue.
My 2002 does this. I have been trying to find an answer. From what I know about my own truck, this is probably what is going on. Thanks for the help. This was the best answer I have come across. P.S. I don't know if there is anything to it or not, but I heard that using Premium can cause me to burn rich and produce too much carbon. Im gonna try switching to Plus or regular to see what happens.
I've been burning regular the entire life of the truck. So, premium gas must not be "my" issue anyway. What do you, "Mad Gomer" think about Lucas Oil Stabilizer?? I got a recommendation to try that between oil changes. Said it helped him?
I've also burned 87 octane during the life of this truck. About 100k miles, and now that cold weather is back, so is the knock at cold start. I have not used the Lucas product, but did try a single treatment of Restore last year, which did not have any noticeable impact. May simply be that multiple treatments are needed, or something with more focus on piston deposits as drbrown indicated in his response, or pull the heads to clean it up & check bores. About to retire my 2000, will see if GM got this fixed on my new one. If not, it's probably my last GM.
Try using a lucas oil additive it helped me alot with the engine noise and it only comes back right when the oil needs to be changed again. I think its called Lucas oil staibilzer.
I was told that there is an o-ring on the oil pick-up tube that deteriorates and it takes a minute to get the oil pumping.Mine is worse in the cold weather.Would weather have an effect on piston slap?
My '00 Silverado has always shown very good oil pressure on the gage, even at startup when things are clattering. One thing about this o-ring theory - if it is deteriorating, it will keep degrading to the point that you will probably notice pressure fluctuations getting worse on the gage (and likely you'll be doing some serious engine damage at that point). Not saying this couldn't be a possible issue on some engines, but the piston slap phenomena is very well known in this vintage of the 5.3L. Mine is definitely worse in cold weather, which makes sense given that piston slap is a clearance problem, and the aluminum pistons will "shrink" in cold temps faster than the iron cylinder bore, causing a more noticeable clatter until things warm up & the clearances close back up a bit (plus you get some oil circulating too, which further calms down the noise). By the same token, cold weather will probably aggravate your o-ring situation if it exists, but I believe it would continue to go south over a relatively short period of time & isn't likely to "get better" when warm weather returns. - Mad Gomer
I have a 2001 Silverado w/ 139000 on it and the pinging sound started under warranty and took it in to a dealer and they said there was nothing wrong.Cold weather made it worse.Progessively it got worse. Now it is noisy in the summer.It sounds like a diesel in the winter upon startup.I took it in recently to my local mechanic but it was warm and made no noise so they had no answer. I might take it back and leave it overnight. This is common on early 2000 models as many people indicate on various websites w/ many explantions as to the cause.No more Gm trucks for me again.

If it's the typical GM slap then yes, you'll have to let the thing cool down completely before the mechanic will hear it, and the colder the weather the better to hear it. If he's been around for long though, I wouldn't think he'd need to hear it since this is a pretty well known part of the 5.3L personality. In my 2000 you could hear it much better in the cab than from the outside, so if that's the case for you, make sure the mechanic is sitting in the driver's seat rather than you. I sold my 2000 and bought a 2011 with another 5.3L - so far so good on the slap issue (about 23,000 miles, probably too early to declare victory though).
Is it a knock or a ticking sound, I see a main bearing repair sleeve available from fel-pro and a special tool also for that sleeve. The time to replace the oil pump is 5.4 hrs then another 1.5 hrs to replace the main bearings, If its a knock better off to repair it before it destroys the crankshaft journals.
David M is right if its a ticking sound you have sticking lifters, go to your local autoparts store and ask for something to add to your oil to free up your lifters
if it's a ticking sound it's probabaly sticking lifters. Look for some products at the parts store.
I have a 2000 Silverado LT 5.3

The noise is called "Piston Slap". I believe it caused by a bad design of the piston and piston rings where carbon is built up over time, especially after the engine was ran than turned off. It will be more noticeable when its colder outside. The only way to fix this is to pull the heads and soak the cylinders with a solvent.
If it's the typical 5.3 cold start ticking noise that goes away after few minutes it's a fuel knock when you start engine when it's cold it runs on cold idle circuit which richens fuel mixture that creates fuel knock they all do it just some more noticeable
On my 5.3L 2002 tahoe I found location of problem by taking out the spark plugs one at a time & putting a compression gauge on each cylender while engine is cold. It turned out to be the # 2 cylender, from the fire- wall on passenger side. It will have low compression at start up & not full compression after warm up when the knock stops. The i dropped the oil pan & discovered worn bearing caps. I changed out engine from a wrecked tahoe 3.5L vortec also & it does the same thing. The only thing i can think of its to replace the poison rings & cap on the # 2 cylender as this is also the same problem location on the second engine.
Sense motor runs goods after warm up i will just use Lucus oil treatment until this engine goes out then go buy a Ford.
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