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Discussion Starter · #1 ·
When I fire my 2001 Silverado 1500 truck up on a cold start, it'll sound just fine for the first 20 seconds or so then it sounds comparable to a warm diesel truck for the first couple minutes then it pretty much goes away. The sound is like the "rattle/knock" a diesel typically makes. It's got 131k miles. Later tonight when I fire it up to head to work, I will take a video. I am not sure that this is just the common noise the 4.8s make but it might be. Never had one before, always had 3.8 and smaller engines but always GM engines around this model range. Normal, or need the video first?

Side note, my MPG average was 18.4-19.1 up until about mid October where it dropped to 18.1. These figures are across multiple fill ups and the same driving routes and habits. I think it's safe to assume it's because of our lovely winter blend though.

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Discussion Starter · #3 ·
GR2017 said:
What grade of fuel? Same with the highest grade available? Have you checked, replaced or cleaned the knock sensors (if it has them).
87. Around these parts, 93 is $0.70+ more than 87 so I don't mess with it. Haven't done any checking or cleaning to any sensors because I wanted to see if this is just the common noise I keep seeing mentioned. After a couple minutes it does go away. the oil pressure is ~60 on a cold start then normal temp it sits around ~50 give or take a few pounds. No engine light and no stored codes.

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How many miles on your motor? What have the temps been when this happened? On my 5.3 when the temps drop, it sounds similar to what you are describing. After my engine warmed up it quit. I put new intake gaskets on and haven't had the problem since. I think the earlier 5.3 and 4.8 had some issues with intake gaskets. Replacement gaskets are thicker than what came stock on the earlier engines.
 

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2001 GMC Sierra 2500HD CCSB
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Sounds like my truck which I am assuming (hoping) is piston slap in my case. I suppose the 4.8l could develop it as well, and you have an older truck which were more prone to it. Typically piston slap will sound worse when cold or when the engine is cold (first start up) and should go away or quiet down a lot once you are warmed up.

Is it definitely coming from the bottom end of the engine?
Was the squeak in your video the fan or a belt?
 

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Discussion Starter · #10 ·
Gozzie said:
what weight oil are you running ? Same as always or have you changed.
I just bought the truck in July I think, and have done 2 oil changes on it, both 5w30 valvoline in the maroon jug. I pulled apart both filters and search the filter medium for any visible wear metals and fortunately all of the pleats were very clean, nothing in them at all. For this second oil change I added about 8oz Lucas (oil stabilizer? .. stuff was thick as tar!) And there's no difference.

My wife's Buick on the other hand black grit.

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Discussion Starter · #11 ·
silentbravo said:
Sounds like my truck which I am assuming (hoping) is piston slap in my case. I suppose the 4.8l could develop it as well, and you have an older truck which were more prone to it. Typically piston slap will sound worse when cold or when the engine is cold (first start up) and should go away or quiet down a lot once you are warmed up.

Is it definitely coming from the bottom end of the engine?
Was the squeak in your video the fan or a belt?
Umm so here's the thing with the obnoxious squealing. I have a long metal rod that I use to listen to every component with bearings and the only thing that sounds a little off -but still smooth- is the ac compressor. I don't see why the belt would squeal for fun, so I am absolutely stumped on what to do aside from replace the belt and I am not a fan of throwing parts at a problem hoping one of them is the fix.

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