Engine knock a 500 miles

[Clint GEFFERS]

On 10/18/2019 at 7:13 PM, bass mechanic said:

 

Have any of you head a faint low frequency engine knock at idle from under the truck?

Seems like it doesn’t happen all the time but occasionally after it’s been driven and I start it up again.

 

 

Sent from my iPhone using Tapatalk

 

Yes since day one and it gets louder as the engine reaches operating temperature. Had dealership work with GM and after a week they said it's normal. They gave me the ticking printout. I even had the truck put on their computer. I had them pull other new 2020s. The other new trucks did it also. I am stumped!!!

[crosslakejohn]

see attached file; released by GM mid feb 2020

gmc 2020 duramax belt rumble.pdf

[dwoods123]

41 minutes ago, crosslakejohn said:

see attached file; released by GM mid feb 2020

gmc 2020 duramax belt rumble.pdf 1.7 MB · 3 downloads

Hmm, reading this does not fill me with confidence that it is the same thing being described here in this forum.    We noticed ours gets louder based upon oil pressure readings on our truck.  Very strange!

[crosslakejohn]

this....

[Capt.Wackencracker]

That's the exact location I picked up the noise with my stethoscope! 

Don't see any drive belts nearby.

[newdude]

Heads up diesel knocking folks:   

 

Quote

 

#PIP5711: 2020 6.6 L5P Duramax Warm Engine Idle Knock Noise - (Mar 3, 2020)

 

Condition: Customers may have a concern of a thumping or knocking noise coming from what sounds like the rear of the engine.

 

Cause: Characteristic noise being amplified by the transmission bell housing.

 

Correction

The noise described in this communication is audible in the interior and exterior of the vehicle but is more pronounced in the interior.

The noise is easiest to duplicate under the following conditions:

Engine at idle (about 600 RPM)

Engine oil temperature 113 - 185 degrees Fahrenheit (45 - 85 degrees Celsius) 

Transmission in P/N

HVAC fan off

Radio off

 

To verify this is the noise described in this PI, remove the accessory drive auxiliary belt.  If the noise level is significantly reduced it should be considered characteristic of the 2020 MY truck and no further repair attempts should be made.

 

Engineering has provided the following procedure for belt removal, testing and installation:

1. Remove the air cleaner housing.
2. Remove intake air duct.
3. Separate the charge air cooler (CAC) tube and position aside.
4. Remove belt and position aside.
5. Install CAC tube.
6. Loosely place air box and intake duct back in place. (So you don’t set a code for sensor when starting.)
7. Start engine and verify noise is gone.
8. Remove loosely installed air box and intake duct.
9. Separate CAC tube.
10. Install belt.
11. Install CAC tube.
12. Install air box and duct.
13.  

Note: Do not run the vehicle more than three minutes without the auxiliary belt installed. Do not raise the RPM higher than idle with the belt removed.

This noise has no short or long term effects on the engine. Do not attempt repairs for this noise.

 

The short of it is...take it in, have them pull the belt.  Have them run it with you present if possible when the belt is off.  

 

Edited March 5, 2020 by newdude

[crosslakejohn]

7 hours ago, Capt.Wackencracker said:

That's the exact location I picked up the noise with my stethoscope! 

Don't see any drive belts nearby.

yeah but that GM document on belts/pulleys might help someone, so I posted it. It's not as if GM is on these forums providing concrete course of action for owners with noisy trucks or even basic info.

That photo displays the source of the thump at idle on my new truck.

I had to check twice, but you are correct!!! No belts nearby.

[Tomato]

I wish they had a section regarding: "If the noise does not stop..."  Has anyone done this at home or at the dealer to check it?

[Scottly]

[FS CHEVY 3500]

My 3500 makes the exact same sound very annoying compared to all my other duramax.

[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'll get my stethoscope out & will be all over this engine like a monkey on a muffin if there are any noises.

If you guys can let me know what the oil pressures are that you have been seeing at different temps and RPM's, that would also be a help because I'm curious to hear that the noise was less after the new oil pump was installed.

Also state whether the oil pres reading is from the dash gage, dash digital readout, scan tool or a master gage installed into the oil gallery somewhere.

There is always an explanation when something is different than it has been before.

[ArtK]

I just picked up a Denali built in mid February and it is making the same noise.  To me it does sound like it is coming from the fan clutch.  I hope there is going to be a fix soon, definitely very annoying.

[Joe mash]

I just purchased my new 2020 duramax. With 600 miles on it. it now has a loud thumping noice at an idle after it warms up. I have owned a view never had this noise. Any suggestions?

[20L8TSierra24]

Man, I've had the itch for a new High Country lately but I'll wait and see what happens with this knocking. I couldn't live with that noise! It would drive me crazy!

Edited April 11, 2020 by 20Bowtie14

[Colossus]

Hey it's no big deal unless it gets worse over time.  Many of us old timers on this site remember and lived with the cold start knock and piston slap that was very evident on the 99+ 5.3L & 4.8L engines.  Most of those engines ended up serving us just fine with no long term effects. 

Edited April 11, 2020 by Colossus