6L V8 noise on cold start - Bottom end bearings v Lifters v Piston slap v Oil pump

[vombil]

hey guys picked up a 6L and knew it had a bit of noise on cold start - seller presented it twice, both times he had hit the key briefly.

weird thing is that I drove it nearly all day I bought it then cold started it the following morning or even two mornings later and no noise.

I've left it a week now and crikey - it's quite the noise! - so I suppose lifter bleed down is the most logical explanation however -

the noise starts loud and has a bit more of a knock/tap than a slap, rattle or tick.

The noise was shocking for about 3-5 seconds - the knocking part - and then the noise became a bit of a slap/tick? and did get progressively quieter over about 30 seconds and was gone after a minute lets say. Whisper quiet when right up to boiling hot with fans on etc

I don't know what oil it's running. I'm going to drop oil and check for bearing material which I've experienced in a 5L VS with big end knock. I'm thinking I'll go to a 10/30. It's a very very clean car with 140 kays and has intermittent service history in the book but does not 'breathe'a puff of any blow-by at all and the underside of filler cap is really really clean.

So how will I determine if it's a fractured oil pump gear, lifters, a big end or just garden variety slap/gudgeon noise etc? - without pulling it down
thanks guys

 

[moveage]

You may already know this but Roadside Assist won’t collect your car from home and take to workshop so may as well prepare for the worst and best outcome by getting more specific noise vibration and harmonic data before she sails away on a flatbed I reckon. Else may solve / narrow down the issue
A rooted big end or rod bearing or bent rod or pushrod or rocker or cam lobe won’t go away at temp. And you just wouldn’t drive it like that so fact it (possibly) disappears sounds like a serious lubrication issue either leak / crack causing a lifter not to pump up but not enough info.
Just to get a baseline, going heavier grade is the wrong direction to assist amateur diagnosis of the issue. Drain and examine oil and filter fill with 5w30 that has zinc (zddp) in it, consider sending off a sample of the oil for $50-$100 to one of several Aussie labs that forensically will tell which metals are getting more wear vs normal. Hence narrowing what’s stuffed if anything.
Anyway thing is drive by wire ecu won’t start with accelerator all the way to the floor so is a good way to check / prep slack lazy leaking lifters to pump-up: foot to floor and turn over three or four times, listen to cadence (how often it knocks) do that a couple of times noting any noise reduction etc.
Now open bonnet (and garage door for ventilation), hook into the OBD port with a scanner that reads Engine Oil Temp and pressure. Prepare phone camera for taking 5-10min video, lights, camera… START car using key only and stand in front of engine bay making notes to camera your observations of noise type like knock on mahogany or squeak, fart or high hat ting as EOT rises above 40°. THAT is the aim here. Coolant temp means FA but obviously note odd movement.
Ideally ask someone to get in driver seat while you listen around engine bay and very slowly increase idle to 1500 for a few seconds noting change to noise and vibration and oil pressure.
Close bonnet and take it for a normal drive (not far from home) noting both EOT and noise.
Lift bonnet with engine still running carefully scan engine bay for location of noise. Note EOT and oil pressure at idle.
Armed with that info you will be in a better position to evaluate next steps.

 

[Reaper]

I had a LS3 lunch a lifter in a *very* bad way some years ago. Took more or less the entire motor with it. Haven't heard of lifter problems in the 6L motors but every one I had did talk to you a bit. Oil pumps can go bad on those motors - I'd be changing that + water pump etc to begin with and hope like fk you haven't damaged any of the bearings coz low cold start up oil pressure.

 

[vombil]

I had a LS3 lunch a lifter in a *very* bad way some years ago. Took more or less the entire motor with it. Haven't heard of lifter problems in the 6L motors but every one I had did talk to you a bit. Oil pumps can go bad on those motors - I'd be changing that + water pump etc to begin with and hope like fk you haven't damaged any of the bearings coz low cold start up oil pressure.

thanks for the reply. so what's your theory on it being low on oil pressure ? If it was a pressure issue wouldn't it be noisey on every cold start? this is only noisey if not started after 4 days or so. I would have thought the engine couldn't drain much more that it would after sitting for 24 hours - esp with thin az 5/30 in it. When I've had pressure issues there will be a light (VS series) and it would knock on every cold start - even if restarted on the same day.

 

[vr304]

Chuck some nulon lifter free in your oil and see if it helps, it is good stuff

 

[moveage]

So you checked the oil pressure reading then?

 

[vombil]

So you checked the oil pressure reading then?

i haven't - everything I read says the pressure warning light will come on immediately if there is a pressure issue. I need to find an adapter - don't think I have 16 x 1.5 in my kit

 

[moveage]

So if you’re ruling out oil pressure then why concerned about pump or oil grade?
You need to get to bottom of this methodically I think else is a waste of time and money. If you don’t have an OBD interface “elm” translation to a phone app then that’s a cheap easy first step n

 

[vombil]

So if you’re ruling out oil pressure then why concerned about pump or oil grade?
You need to get to bottom of this methodically I think else is a waste of time and money. If you don’t have an OBD interface “elm” translation to a phone app then that’s a cheap easy first step n

I have a mate with a really expensive snap on scanner but I'm not all around how to harness it's power lols. I'm definitely going to take a manual oil pressure reading. my gauge has a super long flexi hose so I'm a little doubtful that it will be accurate right at the outset of cold start when noise it at it's worst. I know a bloke with a performance workshop who had changed 5 or so oil pumps that cause a rattle slap at cold start and throw no warnings hence the pump making it to my list of differentials.

 

[moveage]

Did you know that you can drive into SuperCheap and ask a tech to either check the oil pressure or show you how to check it using OBD it for ~$20 plus the ELM?
Without either a video of the event capturing the noise in some shape or form or any hard data in black and white, is not just anyone’s guess what it is, it’s logically a waste of time.
First step is to pinpoint where the noise is coming from and why, to do that you need to gather something to work with as above - video and or oil pressure reading.
I mean could be any moving part and not even part of the engine!