Old Veteran Car Dude

Ok, this is a 2010 Cobalt SS Coupe, 29,000 original miles (yes, I don't get out much). I baby my car, I use the correct weight synthetic oil. I don't over-rev, I don't miss shifts. I warm the car before driving. I let it idle for 5 minutes before turning off (turbo cool-down).

So twice now, when I start the car I hear a rod knock for about 1-2 seconds. I know what rod knock sounds like. It is definitely not piston-slap.

WTF? Has anyone else had this issue? One time I had the "empty coffee can full of nuts and bolts" sound at start-up and I was told it was the timing chain tensioner. Only happened once, sounded like hell.....

But the rod-knock at start-up is not something a new car should do. I know it's a Chevy but damn.....isn't the engine engineered in Germany? Built in Germany or USA...hell who knows.

If others have had this happen please let me know, if not I'll just accept it as good'ole American UAW Union built Chevy quality and keep driving.

Old Veteran Car Dude

joshcsepegi

Just wondering could it be your high pressure fuel pump. That bastard is loud sometimes.
Also the timing chain tensioner is hydraulic and needs oil pressure yo have props tension.
Other than that I hope it's not a rod knock

blueLNFftw

iTrader: (16)

I have never heard of occasional rod knock. Every motor I have ever blown that caused knock was unmistakable and constant. It didnt stop, well, until the rods came out...

ECaulk

iTrader: (6)

Couple questions and a couple statements.

Questions, still on stock plugs and battery? Are you mod'd and tuned?

Statements, LNF's are direct injection and idling the car to warm isnt the best on the intake valve runners (see thread for an example of the issue--> https://www.cobaltss.net/forums/2-0l...e-gunk-282355/ ), start the car and let it idle for 30sec to a min then drive lightly till shes up to operating temperature. Also our turbo's (if yours is still stock) is oil and water cooled, the 5min cool down after isnt needed unless you just did back to back pulls all the way through 4th gear, let her idle for 30sec to a min again then shut her off.

kxrida2000

iTrader: (12)

If I had to guess id say it the tensioner. Can be pretty loud. You should either have constant rod knock or none

kzak104

iTrader: (1)

vvt actuators dont park sometimes, makes a terrible sound, its fine tho. my car does it from time to time. rod knock doesnt just happen once or twice... then go away.

just learn to love all the weird sounds your car makes and everything will be ok :P

Old Veteran Car Dude

I have owned vehicles in the past, particularly GM, that will have a rod knock at start-up until oil pressure builds. Typically, a worn rod bearing will only makes it presence known if you free-rev it (no load) at certain RPMs. The first aluminum block, iron head (yes, that's right) Cadillac HT4100 V8 engines were notorious rod-knocking, rod-throwing, block-busting pieces of sh*t.

A REALLY bad rod knock (bearing completely gone) will knock even at idle, without having to rev the engine. Under load = no knock. No load = knock.

The reason I say "rod-knock" at start-up (goes away once oil pressure builds), is because it sounds different than the tensioner noise that I have heard before. The tensioner noise is constant until you get oil pressure. The noise I'm hearing is 2-3 thumps before I get oil pressure. Thinking about changing oil viscosity and see what happens.

Old Veteran Car Dude

Spawne32

iTrader: (1)

ive had this cause violent shaking as well at idle on a cold start lol