I have a severe knock in my 2002 Silverado 1500 but only when I start it up. The engine knocks extremely bad but then when I shut the vehicle off and restart it the knocking goes away every time . The oil has been changed every 3000 miles since it was brand new. Any suggestions on what it could be and how it could be fixed? The pickup has 105,xxx miles

 

piston slap is a knock condition that occurs only when the engine is cold. once the pistons warm up and expand the noise goes away.
hard to say without hearing the noise. I've had 2 motors with piston slap. for most piston slap conditions...let it warm up for 2 minutes before driving away...don't drive it hard until it warms up and you will be fine.
most manufacturers say it warrants no repair. if you must...the fix is a engine teardown and rebuild.

 

I had to replace 2 pistons in my 2000 sub 5.3 because of that, both were .002" undersized. Thanks GM..........

 

So I shouldn't worry about it as long as I let the engine warm up?

 

if it goes away after warm up your ok. if the knock is there all the time...its time to consider options.

 

thank you

 

I see no-one else has mentioned this, so I will. With a cold engine, and during a first start-up, there is a lot of clearance not only with pistons, but with rod and main bearings. If a main bearing has worn open, that could cause the noise you are hearing. That noise would go away as the engine warms up. A rod noise sticks around.

Did the truck ever blow a head gasket, or otherwise get antifreeze in the crankcase?

It might be worth it to use an oil pressure tester screwed into the side of the block to see what kind of oil pressure you are showing.

 

the truck has never had any head gasket issues. I had the oil and coolant tested to be completely sure and the results were good so no head gasket issues.

 

I'm about to light up some medical cannabis and see what information i can glean regarding your issue from the One who visits in the smoke.

Is there any chance you could record / post a video with the truck making the noise so it would help pinpoint what the problem might be?

Here is a test you could do. With the engine running and making the noise, you could pull one spark plug wire at a time. If the noise quits on a particular cylinder when you pull the plug, that is your problem cylinder.

You could also just let the engine idle until it gets warm, and see if the noise goes away, instead of shutting it off and restarting it.

 

I remember that when the 5.3 L replaced the 5.7.L. What were the engineers thinking? Why didn't show up in the testing of the vehicles with the new 5.3 l?