2007 Yukon Denali (84k) Temp Knocking Sound - Cold Start when Driving

[Polomintus]

Hi all,

This is my first post, and hopefully not my last, I’ve combed the internet and this seems a very solid forum for GM owners, so I’m looking forward to becoming part of the community now that I’m a Yukon owner in Eastern North Carolina. Which leads me to my first post and question.

Two weeks ago I bought a 2007 Yukon Denali 6.2l V8 84,500 miles on it for my wife, traded her 2002 Tahoe LT for it. Overall, I’m very pleased, the car is in excellent condition and has cosmetically been very well looked after, and everything inside works (fingers crossed) at the moment. Here is my observation, when I cold start the engine (first startup of the day) and then drive, I’ll hear a knocking sound, not a tapping, but a clunckish sort of knocking sound and it is defiantly coming from the engine, can be heard inside the car, and louder outside (windows down). Thought at first, it was piston slap, but after reading here and elsewhere, I’m not so sure anymore, because the sound is not there on idle or when I rev the engine during startup, it is only when I drive it.

The sound is at its loudest if I start up and then drive right away (I did this only to test, normally my wife starts and drives after 2-3mins and drives like miss daisy). As I drive the sound does starts to fade, quickly at first to a slight knock, but then stays for just a little while longer, until you cannot hear it at all say after 2-3miles, it seems to collate with the speed of the engine, After it warmed up, it is good for the rest of the day. Current outside temp (70deg) at the moment. After the engine has warmed up, it sings, I've never seen any smoke of any kind on startup, acceleration or idle. Oil Pressure is 50 on startup, when warmed up, idles at 20, when running or above 1000RPMs the oil pressure returns to 40 dead on, this I’m monitoring while driving to make sure. I will say this, on idle (@5-600rpms) it is a little rough, I mean very slightly, but enough to feel in the driver’s seat, but after say 10mins it is smooth. My thoughts are at the moment, a lifter making the sound, I know after reading, this a problem on higher mileage GMCs, my wife’s previous Tahoe did it, but only in the winter days here, and certainly it was not as bad as this, or noticeable at this time of year.

My options at the moment seemed to be, let GM take a look. see if they can see can ID the problem by doing a diag on cold start ($79), the guys seemed ok at the local dealership, where I took it right after I bought it (week ago)and asked them to run a 85K service on it. After asking them to double check it, 40mins, they said it was good and no issues could be located, but that has got to be a light check in terms of finding any issues, and certainly will not be able to notice the sound I’m investigating on cold starts.

The other option in my mind which I think is shoudl do is, run a (Lucas Deep Clean) through it, GM dealership said they recommend only this product on their trucks, rather then seafoam etc.. I’ll comply, to for now. I'm hoping this will address the rough idle issue and remove that from the equation, so as not to associate it with the sound i'm hearing. I will add, since we’ve had it, we’ve done 500miles in two weeks, no issues, we have always used BP RON92 (the premium stuff) and will continue to do so while we own it, but who knows what the previous two owners used. On top of that, I’m thinking of switching to Mobile1 Full Synth, just to see if the issue is with oil not getting to the lifers, or elsewhere. I also read that higher mileage GM engines of this size can have issues with the oil pick up o-ring causing the delay in oil to the top side of the engine and hence the sound.

Love the vehicle, drives very well.

So my questions to those of you with the know or owners of the same SUV, is anyone have, or know what this could be?
What are the best options available to me, rather than just throw money at it.
Mobile1, is it a good solution (synth oil) for the 6.2l V8?
What is a good choice of oil filter to use, I mean top choices?

Thank you for your time in advance, and I hope that this can help someone else in the community in the long run also,

Cheers - Polo

 

[GM Customer Service]

Polomintus,

As you suggestion, it may be a spark knock issue. I encourage you to consult with a certified technician for a physical inspection. They will be able to offer a more accurate diagnosis after doing so.

Please keep us posted.

Louis
GM Customer Service

 

[Polomintus]

Thanks Louis,

I did speak to GM about this, but back when i originally though it was associate with Piston Slap. Their advice was sound, first try the Luca Deep Clean, see how that help with the possible carbon build that the TSB in October 2011 relates to this issue. If that didn't work then they suggested the Cold Start Diag, and then the GM top Engine Clean process. I will ask them on their advice with the updated information and post when I haev an updated.

Would be intrested in reviews of Mobile 1 Synth in the 6.2l V8 and the best Oil Filter to use. As well as any opinions related to my investigation.

Thank you once again,

Polo

 

[Fast55]

I seriously doubt that it's anything but piston slap. My Tahoe has the exact same symptoms that unfortunately started at only 12K miles. I have always used Mobil 1. Little to no noise at idle or reving the engine, but put it under a load, and there it is. They will not touch it under warranty as it is considered "normal". That is exactly the same condition in my work car, an Avalon with the 3.5 V6 that is notorious for the problem. No way it's spark knock if it goes away. If anything, it would get worse as it warmed up and you put more load on it. Like Toyota, GM is aware and I'm sure would be happy to rebuild it at your expense. There is no other solution but to install pistons that actually fit the bores.

 

[Polomintus]

Thank you Fast55,

That was my problem for thinking it was not Piston Slap, in almost all case i could fine, everyone pointed out it was on startup and while on idle. I didn't see anyone mention when the engine was engaged and under load, so thanks for sharing that vital bit of information. I think that’s a very good description with the term "underload" and that my issue is only for a short time from cold start and driving away.

To be honest, if I could have a guarantee that it was piston slap, I’d be content with the sound. I do however still think in the back of my mind "is this a serious crank/barring issue" that wil require an eventual teardown.

Thank you for the input as well on Mobil 1, I think I’ll use it, just because I’ve used it in Europe in my Audi and here in my Jetta, and i've found it flawless with over 190k with those two cars. I just didn't know if you could use synth in the mighty US V8 engines.

Cheers - Polo

 

[gilbo]

Polomintus,

As you suggestion, it may be a spark knock issue. I encourage you to consult with a certified technician for a physical inspection. They will be able to offer a more accurate diagnosis after doing so.

Please keep us posted.

Louis
GM Customer Service

hey louis just curious, what has GM done to correct the piston slap issue, are they quietly replacing engines on case by case basis if a owner complains loud enough, so they don't need to issue a massive recall

 

[felixgun]

I read your description and it sounds like just another case of piston slap... dealership/GM will say "this is normal"... which is complete ******** IMO.

 

[Fast55]

I read your description and it sounds like just another case of piston slap... dealership/GM will say "this is normal"... which is complete ******** IMO.

It is complete ********. They know however, that it's highly unlikely the motor will grenade within the 100K powertrain warranty and even if it does, a short block will not cost them much more than paying a dealer to tear it down, bore it over, and put in new pistons. At least these are nowhere near as bad as the 3.5 in my Avalon. The damned thing sounds like a rod is about to come through the block until it's been running for at least 15 minutes, far past reaching what should be full operating temp. Needless to say, they're all done in my book.

 

[Polomintus]

Thanks for your views guys,

I'm on the fence, i'm by no means a mech, but do share your veiws. First, if i had spent a ton of money on a truck (new), I would want, no i'd expect perfection without compromise... And, with the world we live in, technologies in todays engineering should not produce these types of issues. But on the other hand, the amout of actual truck owners who had documented this sound since early, mid or later on in the engines mileage, who've then gone on to do 150-250k milage with no issues, reassures me this is not going to 'Grenade' on me. That said and done though, for such a fine looking SUV/Truck this sound on start up is annoying and i just want to ensure that my wife and me little sprog don't break down in the middle of nowhere.

I'm waiting on my wife to use a full tank at the moment (she drives does very little miles so i might have to use it up myself) then run the Lucas Deep Clean. If that doesn't work then i'm going to get GM to do the top enginer clean (and add Mobile 1 and decent filter).

With this results i'll report back on any changes in this.

Cheers - Polo

 

[felixgun]

Sounds good. Let us know if that works or at least helps.