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But did not happen on my 5.3L with either product behind M1.Just a guess but I think HPL could remove piston deposits based on @OVERKILL finding carbon after using Mobil 1, which at first I did not believe (not that I didn't believe OVERKILL but that Mobil 1 left stuff behind).
I think when Valvoline is saying no other oil can do this, it's based on the dry off shelf oils. Dry as in little ester/solvency. If HPL has as much AN/Ester as some say then its certainly possible HPL could remove existing piston deposits over time. Amsoil SS too.
Perhaps engines have a greater role …
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