Hello, Your knocking problem is most likely due to piston slap. The 5.7 and 5.3 engines seem like they can develop this condition rather easily and have had this on two different chev pu's after about 85,000 miles or so. Because of close engine tolerances, these engines require 5-30w oil which flows easily at colder temp and can get into critical areas, such as piston to cyl wall clearance. If a heavier weight oil (10-30w) is used that oil can flow slower and not get the oil to those critical wear areas and allow excessive piston wear creating a looser condition where the piston will rock back and forth in cylinder as connecting rod moves up and down. Unfortunately once the excessive clearance is there there is not much to do about it except a rebuild. In order to prolong life, I would suggest that you make sure correct weight oil is used, keeping it changed every 3000 miles and make sure that you allow enough warm up time to allow piston to expand taking up excessive clearance before driving away. Driving away prematurely can cause further wear to take place and this will only allow noise to get worse. I know it sure does make you feel like you have a junk truck, but with a little care and maybe a remote start, it might not be anything more than an annoyance. A little planned obsolence or repairs for GM designed into its future. Perhaps they should put some better skirts back their pistons. Hope this info is helpful bw
Wednesday, January 21st, 2009 AT 12:10 PM
