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Engine knock a 500 miles

bass mechanic
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dwoods123 Enthusiast

dwoods123

Posted
Posted
52 minutes ago, Roadrunner45 said:

To update on the disposition of the repairs.  The good news is the thumping seems to be less pronounced than before but still present. In park and drive at slow speeds it seems a tad bit less than previously. I used to hear the sound through around 4-5 gear that seems to have been corrected at least in the short drive from the dealer to my home. Going to put it to the test tomorrow and tow my 14,,500 pound 5th wheel almost 700 miles. 

I will update of any changes from my first impressions.

I was really hoping this was the fix my service department said that a few with this issue had been corrected by the pump replacement but not in this case. The tech would did the work stated the the bottom end of the engine looked great no shavings in the oil, blue-ing of the rod caps etc.

 

Thanks for the update!  Good to know they did not find any major damage but I was sure hoping the knock would be gone.  

Ours is still as loud as ever but does not seem to be causing any other issues.   Put over 1200 miles on it last weekend with no issues.  

Love the 10sp tranny and the gas mileage we get.  Going to hope it gives us years of worry-free driving!

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bass mechanic
bass mechanic

heres a video with the sounds  

Sask Farmboy
Sask Farmboy

My first chime in for this topic. My 2020 Denali DRW is being built in 2 weeks so I will be checking it out closely. I used to be a Chevy tech and finding stuff like this was my life. I

MN6.2
MN6.2

Didn't they have to change the back of the engine to accommodate the new 10 speed transmission? Doesn't seem like enough to create a knock like that but that is one major thing they changed. 

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Sonny James Enthusiast

Sonny James

Posted
Posted

I have the same what I call "clunking" noise in my 3500HD Denali that got a little louder after putting 500 miles on it.  It is for sure noticeable when standing outside the truck.  The good news is that it's very faint in the cab and as it warms up it pretty much goes away inside the cab.  Especially with the radio going.  So if you no longer hear the noise in the cab, especially after warming up, I would say this is something everyone else has versus being an excessive noise.

KB Chevy Enthusiast

KB Chevy

Posted
Posted
19 hours ago, Roadrunner45 said:

To update on the disposition of the repairs.  The good news is the thumping seems to be less pronounced than before but still present. In park and drive at slow speeds it seems a tad bit less than previously. I used to hear the sound through around 4-5 gear that seems to have been corrected at least in the short drive from the dealer to my home. Going to put it to the test tomorrow and tow my 14,,500 pound 5th wheel almost 700 miles. 

I will update of any changes from my first impressions.

I was really hoping this was the fix my service department said that a few with this issue had been corrected by the pump replacement but not in this case. The tech would did the work stated the the bottom end of the engine looked great no shavings in the oil, blue-ing of the rod caps etc.

 

You say a bit less so does that mean not very noticeable? Do they have any idea what may be causing the thumping noise? I've heard it may be the motor echoing through the bell housing. That explanation seems odd because I've heard others with up to 10K miles with a very faint noise that you have to listen for. Mine can be heard with the radio on at times. And at times not loud at all. It does get louder when it's warmed up though. 

bass mechanic Enthusiast

bass mechanic

Posted
  • Author
Posted (edited)

Ok update I now have 3500 miles on my truck I am the original poster of this thread. My truck is warm and in the garage idling while I add some DEF and I think the knocking has gotten better. I have not changed the oil or anything. Just driving it.
So I took another video while in the garage to compare with the original.


Here’s the original

 

 

 

 

 


I don’t think I’m going to worry about it and I’ll see how it sounds after my first oil change


Sent from my iPhone using Tapatalk

 

Edited by bass mechanic
  • 2 weeks later...
Capt.Wackencracker Enthusiast

Capt.Wackencracker

Posted
Posted

I just picked up my 2020 denali 2500 hd duramax today.

This is my third duramax and my 5th diesel.

I'm 70 yrs.old and been a tech and shop owner most of my life.

Noticed the thump/knock immediately. 

Went to the salesman and listened to another denali diesel.(new)

It was quiet as a baby. Then went to the service advisor and the diesel tech with the same old BS that it was normal and they really couldn't hear what I heard. They said to drive it, and don't worry, it's under warranty.

I think someone should post an email address and phone number we can all flood with our same problem.

There's safety in numbers and Hopefully,,if they get enough owners complaining, they might get off their butts and do some actual research on the problem.

I know GM has changed the lift pumps recently because the Bosch pumps were manufactured for diesel fuel sold in Germany.  The problem was that US diesel was thinner which contributed to lift pumps overheating and creating metal shavings that damaged the engines. Maybe these new pumps might be a good place to start.

Any updates from the forum are greatly appreciated,  and I  will update as time goes by.

Thanks to all who have taken the time to post so far. 

lviv2020 New Member

lviv2020

Posted
Posted

I agree that we should all complain to GM.    Bought 2020 Chevy 2500 High Country in November.  Noticed the thump/knock right away.  Same response from my dealer... it is normal.  

dwoods123 Enthusiast

dwoods123

Posted
Posted
8 hours ago, Colossus said:

well what if it is normal? 

If it is, why do some 2020 Duramax's have and some do not?  Some are much quieter as well but still have it.  Why are there so many different answers from dealers across the country saying all kinds of things?   We are hoping it is normal too and our new truck lasts for years but it is a nail biter for sure when you spend that kind of money!

Tomato Enthusiast

Tomato

Posted
Posted

For what it's worth, and as I mentioned in another post, it definitely sounds like a pump of some sort to me.  I notice that the knock comes on for 1-2 seconds right at cold start-up, then the overall sound of the motor changes (hard to describe, but like a higher idle and maybe a change to injection timing versus compression due to the cold start). Then the knock stops for 2 minutes or so.

 

Also, it seems to be knocking at less than engine speed (could rule out an issue with rotating assembly).

 

If it is not the fuel/lift pump, could it be something with the turbo?  I am not familiar with how it works. Could it be some sort of waste gate "puffing" or something?

bass mechanic Enthusiast

bass mechanic

Posted
  • Author
Posted
1 minute ago, Tomato said:

For what it's worth, and as I mentioned in another post, it definitely sounds like a pump of some sort to me.  I notice that the knock comes on for 1-2 seconds right at cold start-up, then the overall sound of the motor changes (hard to describe, but like a higher idle and maybe a change to injection timing versus compression due to the cold start). Then the knock stops for 2 minutes or so.

 

Also, it seems to be knocking at less than engine speed (could rule out an issue with rotating assembly).

 

If it is not the fuel/lift pump, could it be something with the turbo?  I am not familiar with how it works. Could it be some sort of waste gate "puffing" or something?

the issue with this is 1 undeniable fact, the sound is a deep thud sounds unmistakably either inside the block or if your theory is correct something attached to the block. sounds exactly like rod knock 

Tomato Enthusiast

Tomato

Posted
Posted
5 minutes ago, bass mechanic said:

the issue with this is 1 undeniable fact, the sound is a deep thud sounds unmistakably either inside the block or if your theory is correct something attached to the block. sounds exactly like rod knock 

You don't think it is at too slow of an RPM to be a rod knock?  Too bad we can't connect a timing light to compare.  Or is there a way to connect some sort of tool to each cylinder that tells you when it reaches TDC?

Tomato Enthusiast

Tomato

Posted
Posted

I spent a few minutes with my listening device (stethoscope) and found that the thumping was most pronounced and resonated where I am pointing with the orange handle in the 2 pictures. I do not know diesels well at all, but I believe this is all part of the turbo, right?  Good to note that I did not pick anything up at the bottom of the motor or on the tops of the valve covers. Thoughts?

FDBE0E92-A56B-4041-9AE7-9532CFB284AB.jpeg

Tomato Enthusiast

Tomato

Posted
Posted

This is the second area where the sound is most pronounced.  It is the back tube coming off the top of the motor.

54EDA00B-4DC0-4EF7-AEB0-57AA90C80871.jpeg

bass mechanic Enthusiast

bass mechanic

Posted
  • Author
Posted
1 minute ago, Tomato said:

This is the second area where the sound is most pronounced.  It is the back tube coming off the top of the motor.

54EDA00B-4DC0-4EF7-AEB0-57AA90C80871.jpeg

well if that's true my assessment is if the sound comes from that far up on the engine it is a fuel injector and is likely normal.

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