Proberly just fix itself over time. 
Loud Knock on cold starts
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TECH Enthusiast
Joined: Jan 2010
Posts: 695
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From: Corpus Christi, TX
Loud Knock on cold starts Ok guys whenever the engine is cold usually the first start of the day it will knock really loud then it will go away when it warms up? What could be the problem. Also, could i replace the heads with 243's and and new lifters n trays at 190K miles without hurting anything? Would that get rid of the knock?
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Dude just search before you bust somebody
Piston slap or as it as often called in these motors "cold start knock" is VERY common almost to the point these motors are known for it. Especially the 01 (?) and before motors when they started coating the pistons. The piston slap 99 5.3 in my Z71 is at 229k+ and runs like the day I bought it in 02. Noisy at startup since day one.....OP.... If it goes away within 30-40 seconds at most you are ok...
A rod knock car will stay noisy for a couple minutes or never go away......
Last edited by SOMbitch; Dec 29, 2011 at 09:08 PM.
M1 10W-30 should be OK. A lighter cold weight oil such as a 0W-30 or 5W-30 would help.
Sadly, AC Delco filters are crap these days. Reach for a Hastings, Wix/Car Craft, K&N, Amsoil or Mobil 1 extended filter. They're all pretty decent.
Doing this may reduce the piston slap but as Latch said above, it's pretty common on these engines.
Sadly, AC Delco filters are crap these days. Reach for a Hastings, Wix/Car Craft, K&N, Amsoil or Mobil 1 extended filter. They're all pretty decent.
Doing this may reduce the piston slap but as Latch said above, it's pretty common on these engines.
