Here is a pic from a 2003 Silverado 5.3 with 300k. It broke a valve which caused it to punch a hole in the Piston and trashed the combustion chamber. This truck was bought in 2006 with only 40k and it has always used M1 5w30. I'm impressed with how clean the tops of the pistons are. The rest if the bottom end was just as clean. We believe that a clogged cat is what caused the pressure buildup and broke the valve.
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