Q. You have written about the diesel-type noise found in gasoline engines called piston slap but I don’t recall you writing about the cause. Also, would a certain type of oil help this condition? D.S.

I have a 1941 Packard 120 sedan, and Castrol GTX 20w50 was recommended. Is this correct? Thanks! Sajeev answers: Provided you were recommended Castrol GTX’s classic formulation, this is a good choice.

Question:I thoroughly enjoyed the tech article "When Good Cams Go Bad" (June '06), but I have a couple of questions: If you have an older car without a catalytic converter but don't have flat tappets, ...

Q: I have a 2003 Pontiac Vibe with 135,000 miles on it. This past winter it would knock for a minute or so on a cold start. A GM tech told me that it has a cold piston slap and it will go for a long ...