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My wife's '02 Sequoia has always had a loud tapping/knocking sound from the engine during startup since we bought it in '04. It goes away after 5-10 minutes and usually only can be heard when morning temps are under 40 degrees F. It becomes louder if engine is under strain vs just idling. Is this piston slap? If so, will it cause damage over the long run? Any help appreciated.
 

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It's piston slap.

Read more here: GM Piston Slap -- Like a Knock

It's essentially where manufacturers have reduced the skirt length on pistons (for power/weight/cost) reasons and now the piston (because of geometry) doesn't stay concentric within the cylinder. The problem gets better as the engine heats up and everything expands.

My 03 Tacoma does it, but only when it has been below freezing for a day and I haven't driven in more than 24 hours. Don't worry about it. There's nothing (easily or cheaply) that you can do to change it and most manufacturers (especially) GM are having this issue.
 

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I had a 2005 Tacoma V-6 that did that. Now have a 2010 Rock Warrior with 5.7, does the same thing. Almost sounds like an old chevy with a sticky valve. When warmed up, sounds normal. Anyone else have this?
 

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my 04 DC 4.7 does the same thing...just have to deal with it...
 

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I have a Rock warrior too and engine does the same thing. I had a 2005 Tacoma SR5, V-6 and it did it too. Thought I had a sticky valve. took it to the dealer, and they tried to say it was the electric fuel pump. Took it too a 30 yr Toyota mechanic, and he said because most of engine is aluminum, it just a while for tolerances to be reached, then noise stops. I guess we have to accept something, it still bothers me tho, like an old Chevy engine......lol. He said it will not hurt anything.
 

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238,000+ miles on the odometer and truck has done it since the day I bought it. Still runs well and burns no oil. Noise concerns me as well but so far has not resulted in additional mechanical issues.
 
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