Cold Start Knock

jbutton1462 · May 27, 2013

Hello. I have a 2003 Silverado 4WD Z71 5.3l with 156xxx miles. A couple months ago I noticed a "knock" on cold starts. At the time I was also losing coolant and had a block test performed and it showed that there was no combustion gases in the coolant, so I think the knock and coolant loss are unrelated. Mechanic could not find any coolant leaks and suggested I replace the reservoir cap. But I still have this horrible knock on cold starts. I have noticed that it goes away almost completely after an oil change, but it comes back within a few weeks and gets worse. Right now the noise will last a few minutes until it warms up and goes away. Sounds like lifter noise or rod knock. I am aware of the issues of piston slap and that GM says its "normal", but I have never heard piston slap before and want to make sure it's not something more serious. Can anyone help me out with this? It's annoying and embarrassing!

Carder09 · May 28, 2013

If its piston slap, engine needs a rebuild or replacement. As for your coolant loss, you need to check to see if you have the castech heads, common problem with these burning coolant, http://ww2.justanswer.com/uploads/Bluegorilla/2008-12-05_142924_Coolant_loss_5.3.pdf

GMCDriver1 · May 30, 2013

Should have been around here 10+ years ago. That was a big complaint for the 4.8L/5.3L was piston slap and CSK. Every 5.3L I've owned (several) and one of the 4.8L I had for work would have it when starting the engine up in the morning and then go away after a few min. Somtimes going to synthetic oil helped. It is normal and there are millions of these blocks on the road today with high milliage that continue to run just fine with it. Not to worry.

white1500 · June 2, 2013

What octane are you running? For a while I tried running 87 and my engine didn't like it at all, but now I'm back to 89 and sometimes 91 and it runs a lot better, especially at start up.

And please give us details about your engine oil.