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Hi guys, Looking for some help on a 2008 STS light engine knock in a 4.6 Norstar engine. It seems the noise happens when I accelerate from a dead stop or when accelerating when driving the car. The noise lessons or disappears when you get above 4000 RPM. It could be that the engine noise is just drowning it out but I can’t seem to hear it anymore. Also the noise is louder upon first starting the car after it sits overnight. After about 5 minutes though it seems the noise does lesson and stays consistent throughout the day even if I shut the car off and let it sit for some hours. But I can still hear it. It doesn’t happen at idle and the car runs well. It’s only when I start to rev the motor you can here the noise. I don’t believe that it’s a crank shaft bearing or a main bearing because it would happen at idle as well and certainly would get worse as the car got hot and not when it was cold. But I am not sure and would like to hear your expert opinion on the situation as I’m not real familiar with the northstar engine or Cadillac for that matter. This is my first purchase and try with Cadillac so I hope I didn’t just make a mistake.
 

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2008 STS Northstar RWD, 2000 Trans Am WS6 6 spd, 1968 LeMans convertible 6.6
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281 Posts
I don't hear anything to be concerned about. My N* is a lot louder, she runs just fine.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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71,689 Posts
Don't worry about Northstar rod or crank bearings. The engine may simply need some "exercise" - Google "cadillac forums northstar cold carbon rap".

Run a name brand 5W-30 synthetic oil and a WIX 51522 filter. Follow the OLM.
 

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2006 STS V8 AWD, '95 Ford Ranger
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29,140 Posts
Sounds like you've got piston slap or carbon rap. With carbon rap, conservatively driven cars can have a build up of carbon in the combustion chamber that is truck by the piston on startup and diminishes as the engine warms up. A couple of WOT runs in a lower gear to redline a couple of times will remove the carbon and the noise will go away.
 
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