6.0 LQ4 Rattles like Marbles at low RPM

Dylan Begin · July 7, 2020

I have a 2001 Sierra 2500HD With the 6.0L that has a sound that I can best describe as marbles rattling around low in the engine. Sound is most prominent around 800rpm but can also be heard at idle. Seems to disappear or get much quieter above 1000rpms. Have removed the main belt and confirmed it is not belt or idler related. Have not yet removed ac belt to check that idler yet. Does not appear or sound like it is exhaust manifold gasket related. Truck has 170000 kms and oil pressure is normal. Any insight is appreciated thanks.

diyer2 · July 7, 2020

Well..........

Take your pick.

Rod bearings, main bearings low in the motor.

Could be something else.

garagerog · July 7, 2020

26 minutes ago, Dylan Begin said:

I have a 2001 Sierra 2500HD With the 6.0L that has a sound that I can best describe as marbles rattling around low in the engine. Sound is most prominent around 800rpm but can also be heard at idle. Seems to disappear or get much quieter above 1000rpms. Have removed the main belt and confirmed it is not belt or idler related. Have not yet removed ac belt to check that idler yet. Does not appear or sound like it is exhaust manifold gasket related. Truck has 170000 kms and oil pressure is normal. Any insight is appreciated thanks.

If you can SAFELY access the a/c compressor with a mechanic's stethoscope with the truck running and a/c on, I would for sure check that out. I don't think that idlers or tensioners make the noise you're describing when they go bad. One of the a/c compressors I had to replace on a 04 Bonneville I once had was making the noise you're describing before the compressor went terminal.

Formulabruce · July 8, 2020

The problem "maybe" is NOT a problem. Early 6.0 LS engines had a piston development

Issue and often had piston slap at idle. This was due to the shortness of the piston and silicon of the walls. GM even extended warranty

for this noise way back then. If the engine runs well, and has good oil pressure and doesn't get hot, This is probably the issue.

The truck will run a very very long time with this noise.

diyer2 · July 8, 2020

10 hours ago, Formulabruce said:

The problem "maybe" is NOT a problem. Early 6.0 LS engines had a piston development

Issue and often had piston slap at idle. This was due to the shortness of the piston and silicon of the walls. GM even extended warranty

for this noise way back then. If the engine runs well, and has good oil pressure and doesn't get hot, This is probably the issue.

The truck will run a very very long time with this noise.

Good to know!