H3 engine knock in the V8

[jman1975]

http://www.youtube.com/watch?v=GF3p1G2YE3Y

starts up fine, slower city driving fine, then when I get up on highway for about 10 mins the knocking starts. It eventually goes away but seems to come back during highway driving. Sound is in the linked YouTube video. Wondering where to start with the diagnosis...

 

[Ghostbuster]

seafoam

Kinda sounds like the ole piston slap issues.

[video=youtube;ZlDDd1H1CXU]http://www.youtube.com/watch?v=ZlDDd1H1CXU[/video]

 

[3rdH3]

I remember that video. I think after a couple of more opinions they replaced the engine under warranty.

 

[jman1975]

that piston slap was with 2500mi on the engine huh... mine just started Friday, engine has 58,600mi on it now, oddly after I filled up with 87 octane gas at a station I don't normally use

perhaps I have bad gas? you can hear in my video the "knock, knock, knock" which is definitely not normal, at least with my V8 it isn't

also, my knock comes and goes, especially when freeway driving is involved

trying to rule out potential causes I've read (i.e. lifter issue, leaky exhaust manifold, etc)

EDIT- just went and restarted it, knocking was still there, but after about 10 mins of idle (and me revving the engine a couple of times) the "knock knock knock" was gone

 

[SuperBuickGuy]

I'd lean towards the lifter issue.... either way, not good, not good at all

 

[Ghostbuster]

So I'm guessing you don't have any type of powertrain warranty

 

[jman1975]

So I'm guessing you don't have any type of powertrain warranty

nope, the truck is 7 yrs old now

going to the dealer tomorrow so we'll see what they find...

 

[jman1975]

the current theory by the dealer is that something broke off the crankshaft and that knocking sound is a piston rod rattling around; changing the oil now so presumably they'll look for something to fall out of the pan? said I was low oil too, strange that the CEL didn't trip if that was the case, had oil on the dipstick when I checked it this weekend

waiting to see what they find out and how much oil came out

 

[Hunner]

They need to drop the pan to really look into things.

 

[jman1975]

the current theory by the dealer is that something broke off the crankshaft and that knocking sound is a piston rod rattling around; changing the oil now so presumably they'll look for something to fall out of the pan? said I was low oil too, strange that the CEL didn't trip if that was the case, had oil on the dipstick when I checked it this weekend

waiting to see what they find out and how much oil came out

2 qts came out. Some how I burned through 4 qts since my last oil change at the same dealership. Wow. So the rattle sound was most likely piston rods... Nothing indicative of a problem until that rattle showed up.

They filled it up with 6 fresh quarts and i'm now participating in a consumption test. Who knows what can come of that. Is GM going to come out and say "yup, that 5.3L V8 is consuming double the expected amount, here have a new engine" ? Not likely.

 

[Best4x4]

I normally get 1qt low on oil between oil changes (every 3k). Good old intake sucking it up. So far I'm at 124k and I use the Dino Mobil oil vs mobil1 synthetic.

 

[f5moab]

piston slap went away when the piston skirt expanded due to heat. It was a very common problem with LS1 engines and after about 2 minutes it would be gone.

 

[f5moab]

They need to drop the pan to really look into things.

I would recommend a scope first to see what is physically in the pan. Dropping the pan is a major pain the rear end since you have to drop the front diff assemly. So hopefully the dealer has a scope.

 

[cgalpha08]

Holy cow, that underside is soo clean!!