5.7L Hemi Ram 1500 rod knock when cold

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^^^ this

Does it have an aluminum block? The AL block and steel pistons have differing expansion rates, which likely is one reason why this noise has shown up on more recent (as in post-80's) engines, along with the shorter pistons. Plus, AL conducts sound better than iron. Also the dealer won't do anything. 10-15 years ago they were replacing some Corvette LS engine pistons with teflon-coated ones to reduce the cold slap, but I heard the coating would just wear off.
 
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Originally Posted By: neo3

Does it have an aluminum block? The AL block and steel pistons have differing expansion rates...


I think you mean aluminum blocks, cast iron sleeves and aluminum pistons. And, yes, the expansion rate is different in many modern engines.

But, mostly, the pistons are just really short and rock a bit in the bore before warming up.

Note: Some modern small diesel engines are now using very high tech steel pistons. But, that's something relatively new and I'd guess there are few of them on the road here in the USA. (it's not at all like the diesel cast iron pistons from a century ago)
 
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Thanks for the information everyone.
The noise seems to lessen or even go away when the ambient temp is 60 degrees on a cold start. So I guess it makes sense that it is the differences in the clearances between components that is making noise. I have used many different oils in 5w20 flavor and different filters from mopar to fram ultra to Bosch. I guess the only options left is to contact Chrysler or ignore it. I would try a different weight oil, but I don't want to compromise my warranty or the mods operation. This drives me crazy, might need to start getting away from Chrysler products...
 
Originally Posted By: butcherman
I appreciate you taking the time to answer a question that has probably been beat to death, it just has me worried. If it is piston slap, does that mean that the piston skirts have already been worn down?


It means they put the piston pin right smack in the middle of the piston skirt. If they had placed the piston pin a little bit higher up towards the top of the piston, you wouldn't be having any piston slap.
 
Originally Posted By: Trav
It could also be carbon knock. Cadillac N* had this problem and it sounded like rod knock. It went away once the engine was warm.
Don't mess with it take it to the dealer,leave it overnight if necessary.


This is common for our fleet vehicles. Even had a guy tell me once "that's going to need a new engine". Lasted 500k miles!

So if it really is piston slap it is usually not a serious problem.

Funny, my brand new 2014 5.7 Hemi is as quiet as a mouse and was even silent with no miles on it.

My 6.1 Hemi with 100k miles on it is also very quiet mechanically.

I would be concerned if it was mine...
 
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