08 5.3 avalanche loud slap(knock) at start up

[pwtr02ss]

I've noticed a slap/knock at start up after the truck sits for an extended period of time and I'm thinking the o-ring on the pickup tube may be bad, allowing oil to back fllow while sitting (I'm not sure if this is possible or not). Either way, When i first start it, it sounds like piston slap/lifter/rob all together for the first few seconds then it goes away. The noise does not return after its been started and sits for an hour or so, its only after the engine has sat for 3ish hours or so. After its warm, I can hear a slight lifter tick, very slightly while in a drive through or something with a wall right beside me. The oil pressure seems to be less than normal when warm, roughly 28-30 at idle where in the past, its been 36-40 range and roughly 50 while driving, now its 42-44. Truck has 180k miles, oil has been changed every 3-4k miles since new (Castrol conventional). I did switch to mobil 1 for one oil change to see how it would do, oil consumption was worse so I switched back.

Question, I've heard people adding a few quarts of oil to test the o-ring. My question is, how many quarts do I add? 2 or 3?

Next, am I even on the right track with the symptoms of the o-ring failing.

 

[swathdiver]

I've noticed a slap/knock at start up after the truck sits for an extended period of time and I'm thinking the o-ring on the pickup tube may be bad, allowing oil to back fllow while sitting (I'm not sure if this is possible or not). Either way, When i first start it, it sounds like piston slap/lifter/rob all together for the first few seconds then it goes away. The noise does not return after its been started and sits for an hour or so, its only after the engine has sat for 3ish hours or so. After its warm, I can hear a slight lifter tick, very slightly while in a drive through or something with a wall right beside me. The oil pressure seems to be less than normal when warm, roughly 28-30 at idle where in the past, its been 36-40 range and roughly 50 while driving, now its 42-44. Truck has 180k miles, oil has been changed every 3-4k miles since new (Castrol conventional). I did switch to mobil 1 for one oil change to see how it would do, oil consumption was worse so I switched back.

Question, I've heard people adding a few quarts of oil to test the o-ring. My question is, how many quarts do I add? 2 or 3?

Next, am I even on the right track with the symptoms of the o-ring failing.

Which motor, LMG or LC9?

 

[pwtr02ss]

Which motor, LMG or LC9?

Iron block. Its been a minute since I've fooled with them but I think that's LC9

 

[SnowDrifter]

How long does it last for? Enough that you can get in there with a screwdriver/stethoscope and pinpoint the location of the sound?

 

[swathdiver]

Iron block. Its been a minute since I've fooled with them but I think that's LC9

Opposite, it's an LMG. Ok, the o-ring could be going bad or your oil is kinda thick and taking a couple seconds more than normal to get around. Could also be the pump. If the oil is the same as you've been using, even with the weather change, you can rule that out.

My motor is the aluminum LC9 and it uses a different pump, less pressure and more volume by 1/3 per revolution. Hot idle pressure is in the mid-high twenties and underway is under 40. The bypass spring is set for 33 psi. This pump is the Melling M365 aka GM PN# 12612289. I say this to let you know that the motor is designed to run with low pressure, the minimum spec is 6 psi @ 1000 rpms or something like that.

Put a fresh filter and some fresh oil in it first. Sometimes the filter can cause this.

 

[pwtr02ss]

How long does it last for? Enough that you can get in there with a screwdriver/stethoscope and pinpoint the location of the sound?

It rattles for about 2-3 seconds until the oil is pumped up to the top. Thats why I was thinking the o-ring

Opposite, it's an LMG. Ok, the o-ring could be going bad or your oil is kinda thick and taking a couple seconds more than normal to get around. Could also be the pump. If the oil is the same as you've been using, even with the weather change, you can rule that out.

My motor is the aluminum LC9 and it uses a different pump, less pressure and more volume by 1/3 per revolution. Hot idle pressure is in the mid-high twenties and underway is under 40. The bypass spring is set for 33 psi. This pump is the Melling M365 aka GM PN# 12612289. I say this to let you know that the motor is designed to run with low pressure, the minimum spec is 6 psi @ 1000 rpms or something like that.

Put a fresh filter and some fresh oil in it first. Sometimes the filter can cause this.

The oil is that same as always. Its been doing this for a while (last few oil changes at least, sometimes no noise, sometimes noise), I just want to find a solution before I start tearing into it, mainly, how many quarts of oil is safe to dump in, yet effective enough to submerse the o-ring for a cold start. I would like to do this prior to oil change so I'm not dumping all the fresh oil out while changing the o-ring, if thats the problem

 

[SnowDrifter]

Mine had a similar issue. Ended up being the bypass valve in the oil filter housing

It could also be your oil filter's ADBV

 

[iamdub]

Mine does the exact same thing except it has to sit for a few hours or a week. If I prime the oil system by holding the accelerator pedal to the floor so the engine doesn't start and cranking it for about 15 seconds, it won't tick when I let it start. I'm banking on a failed lifter.

 

[pwtr02ss]

Mine had a similar issue. Ended up being the bypass valve in the oil filter housing

It could also be your oil filter's ADBV

How does one go about changing that?

Mine does the exact same thing except it has to sit for a few hours or a week. If I prime the oil system by holding the accelerator pedal to the floor so the engine doesn't start and cranking it for about 15 seconds, it won't tick when I let it start. I'm banking on a failed lifter.

Yes, mine only does it after its sat for a while. If its just an hour or so, its starts with no noise at all.

My truck had lifter failure and knocked the cam out of it when it had like 25-30k miles on it. They replaced the lifters with the updated parts, under warranty. At like 99k miles, it had severe oil consumption and they put some kind of screen, a block off plate somewhere, and something in the oil pan. I replaced the valve cover because it started smoking after long distances on the interstate, the pcv was all stopped up. I also turned off the DoD when it had like 120k miles so hopefully its not a lifter