Piston Slap - Anyone have experience with this?

[slow 87]

I have a 99 Denali 5.7L 150k mi. and a on cold start after about a minute it makes a knocking or slapping sound for few minutes then goes away. Then
a few minutes later it comes back for a minute or so.

After reading this post I just changed my oil with Mobil 1 and new filter.
Was due for a change anyway.
Will report back results soon.

 

[UNGN]

97K miles on a 2000 Yukon XL 6.0L and it's piston slapped when cold since new. Don't notice it much in texas, but it slaps loud when we head north on vacations over the holidays.

 

[acoen]

On cool mornings my 87 Toyota Truck has some piston slap until it warms up. Hell the truck is almost 20 years old with 130k miles and no problems. I had a 1969 Camaro with a 327 with God only knows how many miles with piston slap, just don't beat on them when they are cold and you shouldn't have any problems. I don't see how changing to Mobil 1 could help but you never know until you try. I'm with you on this, you buy a new truck it should run quite and shouldn't make any noise, that's why you purchased a new truck in the first place....To have no more worry's. GM should fix every last one....IMO. If the truck is under warranty complain enough an they may just replace the motor.

 

[turbopete]

And...

Talked to the service manager at the local dealer. Good guy.
History:
GM first did some piston replacements with teflon coated (or something like that). Fixed the problem for a little while then the slap came back.
They also did some bore cleaning, but the carbon buildup returned with the slap, big surprise.

The bottom line from the dealer is that the engines continue to live for many miles, even with this "problem".

I just let the truck warm up for a bit. Should be O.K...for now.

 

[slow 87]

Well I changed to Mobil 1 and...
after 3 cold starts 80% reduction of noise.
Now after 1 minute on cold start slapping
only last about a minute and isn't as noticable.
Second wave of slapping is gone.
The engine warm seems to be less noisey.
I am thinking it will help even more next oil change. :smile:
Also going to put some GM top engine cleaner in it at some point. :biggrin:


Thanks for the tips guys!

 

[phillyturbosix]

Thank you thank you very much! :biggrin: Cost a little more with Mobil 1 every oil change in your daily driver but it kills the slap a good amount!

 

[87 Pete]

My brother works at GM, and has a lot of experience with this problem.

He says the main reason it happened was that in an effort to increase fuel-efficiency, they are always looking to reduce rotating mass. As a result, they are using very light/short pistons. The skirts are short too, and this can lead to the piston rocking very slightly and making noise. Another issue, is that the corners of an aluminum block twisted/warped more than they planned. Hence, the #1 cylinder knock on LS1's.

FWIW, he believes that it has no effect on overall durability. Both of our LS1's are still running very strong.

I agree though, it sounds like crap on a cold morning. In my case, it's also a good excuse to tuck the TA away for the winter

Pete

 

[slow 87]

Thank you thank you very much! :biggrin: Cost a little more with Mobil 1 every oil change in your daily driver but it kills the slap a good amount!

No, thank you

 

[87GN_ponykillr]

<----------- I'm in! My 99' Formula has a case of the "slap" I still run Mobile 1 syn, I just give it a good 5 min to warm up each time before I drive it. It stops after its hot but still makes me mad it does it.

 

[phillyturbosix]

It was freezin a$$ cold last week and it was sitting for 3 days.. I started that baby up and my buddy thought I installed a diesel in it!

 

[acoen]

Funny you mention diesel, my Toyota sounds exactly the same when it's freezing outside and sounds that way until it warms up. I don't think there is much you can do about it. Just warm it up a little before you drive it. Shoot hearing about trucks that have piston slap with over 300k on them is amazing.
Guess it proves that it doesn't hurt things too much, unless you have sensitive ears.

 

[UNGN]

My brother works at GM, and has a lot of experience with this problem.

He says the main reason it happened was that in an effort to increase fuel-efficiency, they are always looking to reduce rotating mass...

I would hate to imagine how bad the gas mileage on my wife's Yukon XL 6.0L would be if it didn't piston slap.

I get worse gas mileage in it than I did in my 8.0L Dodge Monster Ram and the 6.0L is down 100 lbft of beautiful torque (and it feels like its missing 200). My old ram would kick this YXL's ass in every catagory except "second and third row seat comfort". If dodge only made a suburban...