Tapping sound in engine bay

[Larryjb]

I know I've posted on this before, but I thought I'd throw the lure out there again and see.

The noise starts up about 5-15 seconds after startup, then quietens again after about 1-2 minutes. It seems worse during cold weather.

I have had this tapping sound ever since I've had the truck, and that is for about 5 years. Originally, it had broken manifold bolts, a leaking head (lost about a cupful every few weeks). The oil pressure would drop a little, but not out of spec, by the time I had to change the oil. The oil was usually black and almost sludgy at the end of each oil change. I removed the heads and had them rebuilt, replacing the cracked one. I replaced all lifters, rods, rockers, springs, etc.

I also dropped the transmission to change the rear main seal. The flex plate had no cracks.

After the work, I haven't lost drop of coolant, the oil pressure stays up throughout the entire oil change interval, and the oil still has a little golden colour by the time I have to change it.

But the tapping still remains the same: none as soon as I start the engine, starts up about 5-15 seconds later, then quietens after about 1-2 minutes.

This is a 5.3 flex fuel.

The main difference in describing symptoms as I search online is that it quite upon starting, then becomes noisy, then quietens as it warms up.

So, any new ideas I might not have thought of?

 

[Doubeleive]

first thing i would do is take off the belts and confirm if the issue is the engine or some other attached component. wont hurt anything to run like that first thing in the morning just long enough for the noise to start or not

 

[Captain Insaino]

Research "piston slap"
The aluminum pistons are warming to fill the bore. I think you are hearing the skirts slapping against the bottom of the bore. Very common on your vintage 5.3. Gm says it's not an issue, within Stevie Wonder tolerences. LOL. My 02 Avalanche did this.

 

[JonnyTahoe]

Both my trucks do it but not more than 30 seconds. Time it exactly probably more like 40-50 seconds.

 

[Larryjb]

Research "piston slap"
The aluminum pistons are warming to fill the bore. I think you are hearing the skirts slapping against the bottom of the bore. Very common on your vintage 5.3. Gm says it's not an issue, within Stevie Wonder tolerences. LOL. My 02 Avalanche did this.

I've thought about this. Doesn't piston slap start up noisy? Mine starts up quiet, then becomes noisy, then quietens again. I've tried using the mechanics stethoscope and it seems noisiest at the exhaust side, but I'm not betting anything on that because it could be my impression at the moment. I tried the valve cover, block, exhaust manifold, flange to the Y pipe. There's nothing that breaks my ear drums in all this, but the tapping seems loudest along the exhaust manifold. I'll do more tests soon to see if I can confirm that. I'll also try removing the belts as suggested.

It's frustrating because I have only about 30 seconds to a minute of noise before it quietens down, and then any testing is pretty much done until the next morning.

 

[Captain Insaino]

My piston slap would ease into it over several seconds, then quiet down at about a minute or two depending on outside temps. Not loud initially.

 

[Larryjb]

My piston slap would ease into it over several seconds, then quiet down at about a minute or two depending on outside temps. Not loud initially.

I'm curious. How did you know it was truly piston slap?

 

[Captain Insaino]

There has been class action lawsuits, I believe hundreds of thousands of vehicles have had this issue. It fit all of the commonly known symtoms. Do some research. "Bob is the oil guy" has decent info as well as other sites like LS1 Tech.


https://www.google.com/search?sourc...LjEuMS4xmAEAoAEBqgEHZ3dzLXdpeg&sclient=psy-ab

 

[Larryjb]

I have done a lot of research on this, and it does fit the symptoms of piston slap. I usually like to get a definitive diagnosis if I can, without tearing the engine apart. Dealerships have gotten diagnoses wrong by just listening on test drives.

One test that might be more definitive is to stick the stethoscope on the side of the block. I may have done this before, but I cannot remember because I'm usually trying to rapidly listen to different parts before the tapping stops. If it is piston slap, I should be able to hear it more clearly here.

To tell you the truth, I'm not that worried about piston slap, but if it just happened to be something else really simple and easily repairable, I'll do it.

 

[89Suburban]

exhaust manifold leak?