Knocking on cold start up

[roush611]

Anyone else have this issue? Just bought my 03 Tahoe z71 about a month ago. It seems that the PO did not take very good care of it at all. First oil change was ugly and it had supposedly only been three months. Since that oil change I have put 1k on the it and the oil already looks toast. Recently I have been getting a knocking in the morning when I start it up. I will start it and it will sound fine. About 10 seconds in it will start a pretty loud knock with a rough idle. If i give it 30 more seconds everything will work itself out and it will be running smooth as butter. Any idea what the hell is going on?

 

[taylorjm]

Chances are the knocking is piston slap. Very common on our engines especially when cold. People have said it can sound like a diesel in the morning but usually goes away after a few seconds once the pistons warm up. If you rev it a little that usually makes it go away too. From what I've read it doesn't seem to affect the longevity of the engine and is more of an annoyance than anything else. You would basically have to rebuild the engine to stop the noise, but people have reported going several thousand miles with it like that and it doesn't affect anything.

 

[doylee4693]

I read on this forum im pretty sure that someone added transmission fluid to there oil and the knock stopped and never came back.Its worth researching at least!

 

[roush611]

Thanks for the responses. I will look into both. I got the oil changed again today just to cover the cheap bases first.

 

[yates ™]

Put an oil cleaner in there before your next oil change to clean the system out and see if that helps out.

 

[magicbus]

One of my 5.3 trucks did the same when one of the knock sensors went bad. My wife's 02 Yukon is doing the exact same thing, I'm just not ready to pull the intake manifold and change them.

 

[taylorjm]

i would stay away from the engine cleaners and tranny fluid option. From what I've heard the engine oil cleaners work great and they remove all the gunk in the engine, and dumps it right into the oil pan. The bad part is that it doesn't all come out of that little hole when you drain the oil. It can end up clogging your oil pump pickup and starving your engine. Just my opinion.

---------- Post added at 12:55 PM ---------- Previous post was at 12:55 PM ----------

so what does a knock sensor do anyway?

 

[02tahoeindiana]

Piston slap. Normal with these trucks. Mine has done it since nearly new, never had any problems. Our 6.2 denali does it too, just a perk of owning one of these trucks.

 

[doylee4693]

http://www.tahoeyukonforum.com/forum/showthread.php?t=41426&highlight=smoke+start

 

[roush611]

Thanks for all the info. I am pretty sure it is piston slap. Just annoying more than anything. Im glad to hear its not an issue that has to be addressed right away.