new strange knock, 2014 AT 5.3L

[tig488]

hi guys, I have a 2014 AT 5.3L with 109K miles.  last week I started hearing a strange knocking noise coming from underneath the truck.  it was during a cold start on a really cold morning.  I could hear it also from the topside.  it sounds like horse steps or empty coconut halves bring hit together, if that makes sense.  its not fast, its actually kinda slow, it goes up a little bit with the rpms.  funny thing is, when it happened I stated googling things and found the vacuum pump TSB/recall so I called GMC.  they ended up replacing it for free and wouldn't you know it the noise stopped. well a week later and its back.  its not all the time.  I got underneath it while it was running but can't really pinpoint it.   it kinda sounds like its from the oil pan.  its time to change the oil so ill start there.  maybe its really low, but I haven't gotten a low oil pressure light lately.

 

[M1ck3y]

I'm no mechanic but it sounds like you could be describing rod knock.

 

It sounds like you rely on a low oil pressure light for maintenance purposes? That's not what the warning light is for; it's there to prevent catastrophic engine damage. 

[CamGTP]

A rod knock would be very loud and by now the engine would have grenaded from it. Plus the oil would be full of metal if that let go.

 

I'd have to hear the noise to try and figure it out better. Just seems odd that the new vacuum pump made it stop but then it came back a little while later.

[M1ck3y]

22 hours ago, CamGTP said:

A rod knock would be very loud and by now the engine would have grenaded from it. Plus the oil would be full of metal if that let go.

 

I'd have to hear the noise to try and figure it out better. Just seems odd that the new vacuum pump made it stop but then it came back a little while later.

 

Horse steps, coconuts halves being hit together? imo that sounds loud, but your the mechanic 

[tig488]

no I don't rely on my light for maintenance.  this engine is notorious for being low on oil one day and full the next. I couldn't tell you how many times I've checked the stick to see it bone dry, add a qt, and drain 8 qtz when I change it a week later. I even posted about it a long time ago.  

 

this isn't very loud,  just barely audible over idle.

[Supreme Pizza]

 

 

 

  Check your water pump shaft for bearing play.

[richard wysong]

maybe you should let it rest longer when you check the oil. its possible the oil drain passages are stopped up somewhere in the engine. I would take it back to the dealer and have them check the vacuum pump

[tig488]

I let it sit until it cools off. its been doing that with the oil for a year or so.

[M1ck3y]

Hows your oil pressure?

[tig488]

oil pressure is perfect, dead center.

 

changed the oil today, drained 6 qtz,  still doing it but doesn't appear to be as loud.  its not continuous.  it does it a few times then stops, then does it again a few times then stops.  I don't get it.  guess ill take it to the dealership and let them see if they can figure it out.

[Supreme Pizza]

1 hour ago, tig488 said:

oil pressure is perfect, dead center.

 

changed the oil today, drained 6 qtz,  still doing it but doesn't appear to be as loud.  its not continuous.  it does it a few times then stops, then does it again a few times then stops.  I don't get it.  guess ill take it to the dealership and let them see if they can figure it out.

 

 

 

If your headed to the dealership then it will be extremely expensive and may not even fix the problem.

 

Before you do that, try "Motor Medic". It takes 5 minutes and might solve the problem.

 

I solved a LOUD lifter tick and a low oil pressure issue with this stuff that costs...... $5.

 

I would flush the motor, and change the oil filter brand, and oil weight to something a little heavier. (check manual for options)

 

I recommend not flushing the motor unless there is a need, and I recommend not changing the oil weight, unless there is a need.

 

 

 

[richard wysong]

it would help if you could get a better location of the noise. take a long screwdriver and use it as a stethescope by putting the handle against your ear and probing with the blade different spots on the engine. check all the belt driven stuff as well as the engine but watch out for the fan blade

[Supreme Pizza]

24 minutes ago, richard wysong said:

it would help if you could get a better location of the noise. take a long screwdriver and use it as a stethescope by putting the handle against your ear and probing with the blade different spots on the engine. check all the belt driven stuff as well as the engine but watch out for the fan blade

 

 

 

 

[richard wysong]

you know thats what the dealers going to do at $150+ per hour. they aren't magicians 

[M1ck3y]

7 hours ago, richard wysong said:

you know thats what the dealers going to do at $150+ per hour. they aren't magicians 

 

They won't even do that. If there's no codes, there's no problem..