Q: Engine knock and bad sounds on start

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Whenever I start up my 2007 Toyota Tundra in the cold there is a kind of knocking in the engine. The first time I heard this I had it checked out and the mechanic said it was “piston slap." Not sure how worried I should be about this problem, engine is running fine 99% of the time. This truck has 70,000 miles on it, is it time to be worried?

Since you describe your issue happening when you first start it cold, I’m assuming the noise goes away shortly after starting. When your engine is running, the internal components are literally floating on oil that is constantly pumped and supplied to them and fill micro spaces. When your engine has been sitting for a while and gets cold, it is enough time for the oil to drain down and out of the passages. When you first start your engine after this, there is a brief time where the micro spaces have no oil pressure, only residual oil. If a part is worn enough it can exhibit a knocking or tapping sound until the oil pressure overcomes it, once again filling the gaps. If the knocking sound you’re experiencing goes away after starting, I would recommend a compatible oil additive. This may improve the situation. It is noteworthy however, that Toyota considers the knocking sound to be “normal”.

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