dpgolf

I have an 08 Sierra 5.3 LH6. Approx 150K miles. Every once in a while, could be days or weeks, I get a ridiculous, and I do mean ridiculous and embarrassing, puff of blue smoke from the exhaust. I have been to several mechanics to no avail. A few notes.
It only happens when the engine is warm.
It seems to happen at highway speeds when I lift off the throttle (AFM related)?
I can't purposefully reproduce it-it's random.
It doesn't smoke at startup or any other time.
Sometimes I can go three weeks without it happening, sometimes it will happen twice in two days.
Once the huge puff is out, it's clear until next time.
I have had the left valve cover replaced to the new style.
I seems like there is a pool of oil that gets dumped into a cylinder somehow.
The engine runs perfectly, otherwise. I have been to a few mechanics and, because of the randomness, they don't see it and don't have a solution.
Any ideas please and thank you?

arthursc2

iTrader: (5)

The easiest places for oil to get into the chambers is valve seals and the PCV system

If you have blocked lifter trays or head drain back holes, oil can pool in the heads and get ingested via the PCV system, or leak past valve seals

Granted, valve seals would be more of a constant burn and would likely happen at start-up, not at random

No catch can on this truck, completely stock oil vapor control?

dpgolf

No catch can and stock other than the left valve cover was replaced with the current design. I'm not sure if the new design replaces the original PCV valve with a baffle in the cover (TSB 10-06-01-008F)? The passenger side cylinder head was rebuilt for a faulty valve seat and the builder (very reputable) didn't mention anything about the valve guides. i.e. he didn't suggest the other head should be rebuilt.

RB04Av

Sounds alot like oil is accumulating in a pool in the intake manifold at the bottom, until it spills over from time to time and gets ingested.

I'd try a catch can first. Pretty cheeeeeeep and eeeeeeeeezzzzy. Pop the intake off and dump out the oil that's already there when you put the can on.

1FastBrick

iTrader: (17)

It will do it when you run it hard!!!
It's likely pooling up in the intake manifold as mentioned.

The valve seals would be more of a daily thing on start up.

You can try a catch can deal and see how much oil you trap before it goes into the intake.

MikeGyver

iTrader: (5)

I suspect the new valve cover. The first engine that I had built had rockers that required the builder to butcher the oil baffles in the PCV valve cover. I had the same smoking symptoms as what you described.

RB04Av

Ultimately, this is probably the ROOT cause of the problem, right here.

About 99.9% of us on here, work on our own cars, ourselves. We gather on this forum to discuss what we find and to help others who have less experience than we do when they ask for help. We can sit here and blabbermouth all day long and halfway into the night about what "we think" your problem is, butt if your "mechanic", whatever that is, doesn't "think" the same thing, NOTHING will ever get done.

STOP with the "mechanic" ELEPHANT PLOP. Either get out there and HANDLE IT, or resign yourself to putting somebody else's kids through braces and college, instead of your own. And making NO PROGRESS WHATSOEVER all at the same time.

While Mike's experience above is insightful, it's not likely to apply to your situation.

If your vehicle has the updated valve cover, then unless Stimpy DESTROYED it somehow (see his comment about "butcher"), it's fine. That said, these engines in general, from the day they were introduced in 1997, have had oil control problems related to the PCV system. Seems that the oil gets whipped up into a vapor in there and becomes uncontrollable or something. Hence the popularity and commonness of catch cans. Seems to merely be a fact of life, for whyever. I suggest you try one, after dumping the pooled-up oil out of your intake. You might actually be surprised how much can accumulate in there: probably a good ¼ of a quart. My truck did it RUTHLESSLY when I had the Castech cracked head thing going on (although that specific issue doesn't apply to your truck), and it truly amazed me how much oil there was sitting all up in there.