could anyone here help me diagnose this cold start noise...

http://media.putfile.com/VQ30-Start-up-knock2
I posted this a while back in the 4th gen forum but didn't get any good replys.
the noise does not appear to be coming from the top end. with the naked ear it is most noticeable from underneath the engine, or from the passenger wheel well. I bought a mechanic's steathoscope and poked around, but it is hard to isolate since it goes away after 20-30 sec. as far as I can tell it is not coming from the TC tensioner (when I probe the tensioner inspection cover, and the larger TC cover, I hear nothing).

can anyone here tell me if this is bearing noise or piston slap? lifter noise? oil pump? could it be spark knock?

some other facts:
- oil: Castrol Syntec 0W30 (a thick 30wt oil)
- filter: OEM nissan
- miles on oil: 2k
- 88k on engine. no sludge. disected used oil filters are very clean.
- GTX oil changes every 3-5k since new.

 

Have you checked your flux capacitor ? I hear it's a common problem with these engines. While nothing specific comes to mind, it certainly sounds like a problem with oil pressure building quickly enough (given the fact that it disappears after a half-minute or so). Oil too thick? Does it occur only after a cold-start, or do you notice it when the car's been off for, say, 45 minutes or so?

 

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the noise is only on cold starts after the car has sat for more than a few hours.

Nmex, what's wavey mean? do you know something about GC that I don't? it supposed to be one of the best oils for this engine in terms of smooth quiet operation.

 

I think he's trying to draw your attention to a possibility. I know the 3.5 calls for nothing but 5W30 and I believe the VQ30DE is the same. I've found that these motors are quite picky where oil weight/filters are concerned...I think many would agree.

 

Well it's a zero weight oil at cold startup so that might be exacerbating the issue. Maybe he should use a 5w-30 or 10w-30 since they are thicker at cold startup.

 

the thing about this particular 0W30 is that it is actually thicker than almost all other 30wt oils on the market (5W and 10W alike) at every temperature (cold and hot). they only call it a 0W because it technically does meet the 0W spec at extremely cold temps. there's a whole forum dedicated to this stuff over at bobistheoilguy.com

having said that, I think I may swap it out for a thinner oil. M1 5w30 most likely. but I really do want to know what the h3ll this noise is.