Low end knock when cold start

[Lorne Sierra Truck]

Been a GM guy forever, I have a 2009 Sierra 5.3L. Been faithful to use quality oil and change every 5000 Km. When engine cold, sounds like a low end knocking noise. When engine up to temperature, noise is gone, engines sounds and performs great. Could this be a bearing? Just turned 200,000 Km. PLEASE REPLY

[Jsdirt]

Sadly, this is the norm for GM V8's these days, but it's hit or miss. Grab 50 identical trucks and:

 

1.) All 50 may knock

2.) None of the 50 may knock

3.) Any combination thereof may knock

 

The automotive industry today is a complete and total crapshoot (Shitshow, if I'm honest).

 

Not knowing your mechanical aptitude, the knock could very well be lower-end rod knock, or, could be lifter knock. As you may or may not know, these engines are extremely failure prone, AND hit-or-miss, with lifter longevity. Most fail between 50k on the low end, to 180k on the high end. The majority seem to average a failure around 120k. Of course this depends heavily on maintenance, and oils used. The lifters are classic low-bidder junk GM tossed in an otherwise fantastic platform - par for the 21st century course, unfortunately for us consumers. They spin in their bores and self-destruct, or lock in either the open or closed position as it relates to AFM (Active Fuel Management - AKA, "4-cylinder mode"). Misfires accompanied by noise and high wear metal levels in the oil are the first clues.

 

Also, the oil pump pickup tube o-ring is another high failure item (among a few other things).