Need advice..Engine Knock

[TWITCH101]

So I bought a 01 yukon 150k from a friend and he told me the knock is normal out of these model trucks so I was like whatever you say I'll take your word for it.

Anyway the motor makes a knocking noise everytime it has a cold start....but after I let the thing idle for about a minute maybe less the knock will slowly go away and then the motor runs smooth. If I start the truck cold and drive it before the knock goes away then it sounds terrible (like a diesel or something) Other than that the engine is very strong, doesn't burn oil, and gets good gas mileage. Also it idles around 500 rpms when warm which seems a little low to me but it may have a chip or something. Its just that initial cold start after the thing has sat overnight that makes it knock. Its not bad while at idle while warming up but I would like to know what the cause is.
My first guess is that a knock sensor may be gone but I'm not throwing any codes on the dash so I don't know where to start.

Just hoping that someone on here has had the same issue or knows what I'm dealing with here.

Feel free to ask any questions if it may help....I'll answer to the best of my abiulities.

 

[07Burb]

This is commonly referred to as "piston slap" and, as your friend stated, is common with these models.

 

[TWITCH101]

This is commonly referred to as "piston slap" and, as your friend stated, is common with these models.

Is it anything to be worried about? should I have it fixed?

 

[07Burb]

Nope...nothing to be worried about at all. I would say that the vast majority of these LS based motors do it on cold start up just like yours does and they will run forever when properly maintained.

 

[TWITCH101]

Thats great....I figured it was alright since it ran smooth when warm but I just liked to know for peace of mind....i searched around online and found the same general consensus that you just gave me from other forums and mostly all said it was nothing to be worried about so I think I'll just keep driving it until I have a problem or make a discovery that could help fix it.

 

[GMC Yukon]

Yep thats the same sound I get after 180,000 miles that I put on her.... I Allways let it warm up and let the oil circulate befor driving her away. Cool starts suck... You mite want to put some good oil in her. I use Moble 1 full synthetic ( Truck & SUV ) Well worth the money! Mine has 237,000 on her now and still runs like a Time-X !

 

[TWITCH101]

I'm a synthetic fan as well as that is all I run in my motorcycle....I'll have to try it on my next oil change

 

[Kman]

YouTube Piston Slap.

Let the truck idle for a minute or two on cold mornings before you drive away.

 

[TWITCH101]

yea I always wait until the noise is gone before I drive...doesn't take any longer than 2 minutes tops.

 

[01HDtahoeNJN]

Not to Jack the the thread but in the winter/colder weather my engine makes a squeal like noise kinda like when a belt is wet...is that normal or okay?

Sent from my SCH-I500 using Tapatalk

 

[afpj]

there's a thread on this forum about using tcw3 2 cycle oil into the gas tank that helps with the piston slap noise. haven't personally tried it.

 

[Diggerdan11]

I had the same problem with my Tahoe i just bought in January with 140k. Its sounded really bad like a diesel until it was warm.

I just wen to Autozone and bought and Additive. I think that brand was CD-2its and Oil Detergent. It worked great and now my engine purrs like a kitten.

When its time to change my oil, im going to go Full Synthetic and They also make additives that you put in in place of one of the quarts of oil.

 

[TWITCH101]

there's a thread on this forum about using tcw3 2 cycle oil into the gas tank that helps with the piston slap noise. haven't personally tried it.

interesting???have a link????

 

[lowAZhoe]

LOL piston slap??? thats the funniest thing i have ever heard guys...ive been working on cars for 10 years and have never told any of my customers thats its normal piston slap noise....

try replacing your oil pickup tube o-ring. remove oil pan, remove pickup tube, replace oring, reinstall pickup tube, replace pan gasket, and fixed. these LS engines the orings get worn and lack oil pressure on startup.

 

[TWITCH101]

LOL piston slap??? thats the funniest thing i have ever heard guys...ive been working on cars for 10 years and have never told any of my customers thats its normal piston slap noise....

try replacing your oil pickup tube o-ring. remove oil pan, remove pickup tube, replace oring, reinstall pickup tube, replace pan gasket, and fixed. these LS engines the orings get worn and lack oil pressure on startup.

How costly is this??? what parts will I need other than the o-ring? for instance will I need another oil pan gasket?

 

[lowAZhoe]

How costly is this??? what parts will I need other than the o-ring? for instance will I need another oil pan gasket?

oil pan gasket, oring, and engine sealant (gm sealnt recommended). pan gasket is about $40, oring is a few bucks, and sealant about $20

 

[TWITCH101]

cool...and its just a simple drop the oil pan and its all right there???

 

[lowAZhoe]

cool...and its just a simple drop the oil pan and its all right there???

yea pretty much. if u have 4x4 u will have to unbolt the front diff and let it drop down...dont unbolt the axles and it will stay up there. crossmember has to come out and then theres a harness on the front with one 10mm bolt, a clip holding trans cooler lines on passenger side and 2 bolts on on each side in the rear holding a plastic filler panel on each side. if u have oil cooler lines there r 2 10mm bolts on drivers side, if not its just blocked off...once the pan is off theres 2 13mm nuts and a 10mm bolt holding the tube to the oil pump in front.

2wd pays us 2 hours, i can knock them out in about 20 minutes...4x4 pays 4 hours, can be done in about 40 minutes....but ive done tons of them...

 

[TWITCH101]

nice thanks for the help...I'll have to try this next oil change which is really soon. How confident are you that it will fix my prob?

 

[chauncey0337]

LOL piston slap??? thats the funniest thing i have ever heard guys...ive been working on cars for 10 years and have never told any of my customers thats its normal piston slap noise....

try replacing your oil pickup tube o-ring. remove oil pan, remove pickup tube, replace oring, reinstall pickup tube, replace pan gasket, and fixed. these LS engines the orings get worn and lack oil pressure on startup.

My oil pressure seems fine on startup. Could there be something else causing this awful noise on cold starts.