Knock when cold

[Denalibro76]

Good morning all you fine folks. I have a 2009 Yukon with the L9H and correct me if I’m wrong but it doesn’t have AFM right? Reason for my post is I have a knock when the engine is cold. Not really noticeable at idle (except initial startup) more noticeable while driving until the engine gets to about half normal operating temp. Not sure if it’s piston slap or rod knock? Since I haven’t experienced either issue before I thought I’d ask you what is more likely?

 

[SpareParts]

Sounds like piston slap.

 

[strutaeng]

Piston slap, but usually that goes away in 30-60 seconds (when cold months around here, but really depends on ambient temperature).

Definitely is not rod knock if it goes away.

Could also be broken exhaust manifold bolt(s) which is super common.

 

[Joseph Garcia]

I've had a similar knock since I purchased my new-to-me 2007 Yukon XL Denali, and it goes away as the motor warms up. I attribute it to piston slap, since I've replaced all of the lifters and installed new exhaust manifolds with ARP bolts.

I just baby the motor, until it is fully warmed up.

 

[rdezs]

If you upload a video with audio..... Piston slap should be 100% confirmed by many of us hearing it. Interpretation of sounds without actually hearing it is very objective. Like the difference between a slap and a knock.

As for timing of the sound, a rod knocking tends to get louder as the engine warms up and the oil gets thinner. Also louder with RPM increases and usually a pretty good oil pressure drop.

While the "official" position on piston slap is that it's harmless..... And this is just my personal opinion that doesn't coincide with the official position from GM..... Is that as a former machinist in years gone by..... Two pieces of metal smacking each other audibly is not good. I view it as a defect in the Piston skirt design, or the lack thereof. Common Sense tells me that if you slap an aluminum piston hundreds of thousands of times against something to where you can hear it, you will begin losing material. Now who knows, this might take 200,000 miles. And that is probably why GM says not to worry about it.

Sorry, a bit off topic, and in the form it's probably been beat to death like a piston slapping a cylinder

 

[Denalibro76]

Piston slap, but usually that goes away in 30-60 seconds (when cold months around here, but really depends on ambient temperature).

Definitely is not rod knock if it goes away.

Could also be broken exhaust manifold bolt(s) which is super common.

Yeah. On cold startups it definitely goes away after a minute or so. I’m going to have to take the fender liners out and have a real good look at the exhaust manifolds to check for issues as I have heard what sounds like an exhaust leak when I’ve started it.

 

[Dustin Jackson]

Is this because it's an aluminum block?

 

[Marky Dissod]

... 2009 Yukon with the L9H and correct me if I’m wrong but it doesn’t have AFM right?
Reason for my post is I have a knock when the engine is cold. Not really noticeable at idle (except initial startup),
more noticeable while driving until the engine gets to about half normal operating temp.

L9H is free of any and all Engine Half@$$ hardware or software bullschidt.

Cap'n Obvious says:
Engine'll likely last longer and age more gracefully if you don't move out of park for a min after starting it,
and drive as gently as reasonably possible for the next five or six min.

Cap'n Obvious might not know that, if you choose the right motor oil and oil filter,
it might actually help minimize piston slap over and above driving gently til it warms up.

 

[Blackcar]

Have 02 Yukon that has piston slap since new. Tried to get warranted when new no go.

I have tried different weights of oil and the one that works best (least noise and quickest slap stop) is 5-W30 semi synthetic.

 

[rdezs]

Is this because it's an aluminum block?

My understanding is GM addressed the problem by coatng the pistons and lengthening the skirt. Lol, not sure if GM would admit that though.... Because that would be admitting there was in fact a problem

 

[rdezs]

.... And I'm sure there's a joke in here somewhere about short skirts? LOL

 

[j91z28d1]

the e38 ecm actually has tables and settings to try and address piston slap. I'm not going to pretend to know what it does, but they are there and labeled something about piston slap.

my guess that's slow why they switched to a injector closing time strategy from opening time on the Gen 3 ecm's.

 

[Marky Dissod]

Have 02 Yukon that has piston slap since new. Tried to get warranted when new, no go.

Too bad GM were building the rest of the engine so well that apparently the piston slap wasn't enough to wear those engines out sooner.

I have tried different weights of oil, and the one that works best (least noise and quickest slap stop) is 5W30 semi synthetic.

Brand of oil, or specific flavor of brand of oil, makes no difference? ANY GroupIII 5W30?

No matter what motor oil I've tried, 1st min of every winter cold start outside, lil bit of piston slap.
0W30 or 5W30 Valvoline, preferably Restore & Protect, with a Purolator PBL 25288 or Mobil1 206.
If I drive like my right foot is broken for the 1st min, only I can detect the piston slap.

 

[Blackcar]

Too bad GM were building the rest of the engine so well that apparently the piston slap wasn't enough to wear those engines out sooner.Brand of oil, or specific flavor of brand of oil, makes no difference? ANY GroupIII 5W30?

No matter what motor oil I've tried, 1st min of every winter cold start outside, lil bit of piston slap.
0W30 or 5W30 Valvoline, preferably Restore & Protect, with a Purolator PBL 25288 or Mobil1 206.
If I drive like my right foot is broken for the 1st min, only I can detect the piston slap.

I use Pennzoil but the semi synthetic is hard to find so probably will go to full synthetic.
I have enough semi for about four more oil changes. I also use AC oil filters my 02 has 65000 miles on it now.

 

[Denalibro76]

L9H is free of any and all Engine Half@$$ hardware or software bullschidt.

Cap'n Obvious says:
Engine'll likely last longer and age more gracefully if you don't move out of park for a min after starting it,
and drive as gently as reasonably possible for the next five or six min.

Cap'n Obvious might not know that, if you choose the right motor oil and oil filter,
it might actually help minimize piston slap over and above driving gently til it warms up.

Yeah I always let idle for 10 minutes or so before I drive in the winter here. What’s the “right” oil and filter?

 

[Marky Dissod]

What’s the “right” oil and filter?

Without objective tests that measure things we care about, and without the data being published so we can compare them, we're gonna keep getting stuff like
"I've been ignoring data for decades about how the brand I trust has been getting worse", or
"I don't differentiate between the different motor oil formulations my favorite brand makes", or
"I ignore any test results that indicate that the OE factory fill's performance has been exceeded by another motor oil", or
"I fail to consider why the factory fill in Europe (or even Mexico) is different from the factory fill in the US" ...

Which is why I think that the motor oil industry is an oligopolistic cartel
(like cable tv companies that bundle the channels so that you have to buy more bundles to get the channels you want).

All that said - even though changing motor oil / ATF / coolant / etc MORE often than the manual says is just as important -
(if you change oil every 5000 or more miles, and you have oil consumption, have you bothered trying changing it before the oil consumption occurs?)
I've been using 'vette-spec 0W30 or 5W30 Group IV synthetic in every GM engine I've ever owned,
and Mobil1 or Purolator PBL oil filters, for nearly 30 years, because I used to drive like a cabbie on meth, and figured I needed extra protection.

 

[EddieC]

Just a spin off, you should hear the piston slap on old Brit bikes I've owned. It's near to a ringing sound.
And it's the least of the noises they make but they keep on chugging.
It takes some getting used to but then something to look forward to.
So my experience with piston slap has never been detrimental.

 

[donjetman]

What’s the “right” oil and filter?

 

[Fless]

Which is why I think that the motor oil industry is an oligopolistic cartel
(like cable tv companies that bundle the channels so that you have to buy more bundles to get the channels you want).

This is a common misconception. The video distributors are tied to the programmers' contracts, many of which require their multiple program streams to be carried on the lower tiers (more subscriber viewing = more income from subs and from ads, etc.). Either put it on the lower tier or don't carry it - gotcha! This is why 'a la carte' programming availability is so scarce; the programmers don't allow that unless they're streaming (and have you seen and priced the streaming packages lately?).

Take a look, for another example, at ESPN on any channel lineup. The contract will probably read that ESPN and ESPN2 are carried, but they MUST be on adjacent channels.

 

[Familyman2112]

I’m glad I happened onto this thread. My ‘11 Denali with 125k has had me very concerned lately. Granted it has been quite cold lately in northern Illinois, but the slap has been very loud on cold starts and tends to take 4-5 to go away. I’m at about 4K on Mobil1 full synthetic. I typically go about 5k on full synthetic, so about another month. However, I have been noticing that my oil pressure has been relatively low. I checked my oil, I was down a full quart. Just to be good, I added a quart. I’m still going to change it shortly. The pressure seems to be better, mostly, but does drop at different times while driving. Lastly, do the manifold bolts make that big of a difference? I had a mechanic replace both manifolds. I kept getting leaks, he kept tightening the bolts, put in new gaskets tried different grade bolts with high heat lock tight. But the leak keeps coming back. Any thoughts would be greatly appreciated.