knocking sound comeing from engine -- any idea guys? had it for a while its just startign to bug me

 

Can you be more detailed, when does it happen, when is it louder, is it the same sound all the time, have you done anything to your car lately that could have started it, how many miles, etc. We can probably help you out a bit more with more information.



Micah

 

on start -up ? --- piston slap... known issue Allegedly not harmful
some claim going to 10W 40 cures it, others claim going to a higher flow filter cures its..... and some claim Royal pruple or Amsoil 5W30 cures it.

At WOT ? pre-detonation ??? any knock codes ?
exhaust rattle ??

 

nope car runs fine it just has a knocking sound when i start the car its not too loud just kinda wondering what it might be

 

My 04 with 15k miles knocks like a diesel until fully warmed up. Neither GM nor any dealers I've dealt with are willing to correct the problem.

I had the engine oil analyzed a few weeks ago. The report came back abnormal high levels of "copper = 218" and "silicon = 72". When I asked Amsoil to help explain the test results, they sent me this reply...

"Subject: RE: OAI report

Thank you for contacting AMSOIL with your concerns.
In response to your inquiry, GM has had piston slap issues with some of their engines, but this was corrected around 2003. It never applied to the Corvette engine, but other V8 models. No technical bulletins have been published concerning this piston slap issue in any Corvette model year as of now. The analysis report did show high silicon and copper. This could be a break in issue, or possibly dirt ingestion and some abrasive wear. If dirt is being ingested into the engine, it will have to pass into the cylinder areas and could cause abrasive wear to the pistons. This could lead to some form of knock. It would be wise to look at the air intake system to see if it is sealed.
Thank you again for the opportunity to respond to your concerns. As always, please feel free to contact us again if we can be of further assistance.
Darryn Wallace
Technical Service Department
AMSOIL, Inc."

I had a good laugh after reading this ( but then again, i'm something of a smartass too). Wow, GM corrected this “problem” in 2003, and it NEVER applied to the Corvette, which of course has the same LSx family engine. Plus the high copper and silicon is from “dirt” that’s somehow getting passed the air filter.

I'll be the first to admit I have no idea what the oil analysis report figures really mean or if there is any correlation to damage caused by piston slap. All I ask and expect are honest and straight-forward answers. Is that asking too much?

 

you have a wierd dirt composition where you drive!!!!!!!!!!!!!!!! and that non existant piston slap......... lots of that in corvettes that i've been told. heck the service manuals describe how to explain it to the customers!!!!!! i sure hope that silicon is not bearing babbit!!!!! and i dont know for sure but... isnt the bearings made of copper/alloy type material??? they use to be. and then a babbit material over it for slickness

 

I'd be concerned with silicon that high, which may airborne dirt, sealers, gaskets, or antifreeze inhibitors. What kind of air filter do you have and when was it last cleaned/replaced? What kind of oil filter are you using? How long was the oil run on this sample (e.g. if you are running your oil twice as long as the next guy, say 6k vice 3k miles, then your silicon and copper levels could reasonably be expected to be higher)? Do you know if the trend in silicon is up, down or constant? If the trend is down, it might not be a concern as it could be material leaching out of gaskets on a relatively new engine. If it is up, it might be indicative of an intake problem (dirty filter or air leaking around the filter), or a growing problem inside the engine such as a coolant leak. Learning this info is why trending is so important and valuable in used oil analysis.

But, those copper levels don't appear to be that abnormal to me for an LSx motor. These guys who were doing an oil test in their Camaro also had what they thought to be high copper levels so they put out a data call which you can see here:
http://neptune.spacebears.com/cars/stories/copper.html

As you can see from comparing your copper to these at about the 15k mark, they are high but not totally out of the ballpark. I do think it is possible that the increased levels of silicon, which may be dirt, could be causing increased wear which is showing up in the copper readings. And again, the trend is important. If the copper is trending down, this may just be normal breakin of the bearing material.

As a comparison for you from a fellow forum members car, this a 99 C5 with 56k miles on it running AMSOIL Series 2000 0w30 for the 6/24/05 and 5/06/05 tests and German Castrol 0w30 for the 3/11/05 test, and a K&N oil filter. His car shows very low levels of copper, which isn't too surprising to me for a car with 56k miles on it running AMSOILs best oil. He is also showing an upward trend in silicon, which may be attributed to his using a Blackwing Intake that wasn't cleaned during this test cycle.
Corvette C5 AMSOIL Series 2000 0w30 Used Oil Analysis Report

 

Thanks for the info SubDriver. This is the type of information I'm looking for. The air cleaner filter may have been the original. It was dirty, but didn't look that bad. I changed the filter soon after receiving the report. The oil was changed at time sample collection was taken.

I'll put on as many miles as I can this summer and have the oil analyzed again this fall. I’m now using Amsoil 10-30 / Amsoil oil filter instead of Mobil 1. Mobil 1 was the oil analyzed in the report with over 9k miles on that change, and the in car computer still reading 20% remaining.

Hopefully the higher than normal readings are simply due to number of miles, and length of time between changes. (14 months?) I'm the second owner, so some of this is guess work, but I believe to be accurate.

Thanks once again for the first class information. It’s very helpful.

 

Given you probably had an old air filter, and that the sample life was 9k miles vs what is more likely near a 3k average on the link I provided above to the other LSx copper results, you probably don't have anything to worry about. I suspect you'll see lower silicon and copper readings on the next report.

FYI, the owners manual (and AMSOIL) both require oil changes at least annually independent of mileage or the DIC Oil Life Monitor reading, so I wouldn't take this oil change past the 12 month point.