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Actually I am not sure if its piston slap or not. I might take it to a dealer to be sure.

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So my truck has 186k on the engine and everything runs fine, no noises otherwise.

I assume its Piston Slap because over the course of the 30 seconds it goes away(Piston warming up and expanding?) Also the temperatures just barely started dropping below 80 or so in the mornings (I was in NC when it was like 45 out at 5 in the morning when I realized it was occurring)

I don't know the full dynamics of this piston slap and wear. Should I be letting it idle for that 15-45 seconds until the noise is gone or does it not make a difference to immediately begin driving?

 

It is probably stretched timing chains and worn timing chain tensioners. Use 5W20 synthetic oil and a Motorcraft oil filter so the oil pressure will build quicker on cool starts.

 

I have 01 5.4 does the same thing. My mechanic told me that the push rod end has become oblong and after oil pressure builds up it quiets down. It drives me crazy!!!

 

5.4 doesnt have pushrods