Huge puff of blue smoke once a month

[SC Dean]

2008 Sierra, 5.3L w/ 150K miles. As the title says, about once a month or so, I will get a huge, and I mean huge, puff of blue smoke out of the exhaust. It's strange that it's so intermittent, and I cannot purposefully replicate it. It's random except that I notice it as I lift off the throttle, never under acceleration. Any ideas?

[Jworks]

I have a 5.3 also but have not had this on it.  However, I bought a used Mazda p.u. years ago.  I noticed that some mornings I was start it and see the same thing you do.  Then it would go away.  I asked my mechanic about it and he said it was a valve guide worn and if the valve stopped at a certain point when the engine shut down oil would drip down in that cylinder.  At crank up the oil would burn off.  Now, that was a 4 cyl Mazda 1988 -- it is not your 5.3.  But I would guess its the same on your motor.....a worn valve guide.  I "may" have experienced a quart low between changes -- that was so long ago I don't recall for sure, but I would recall it if oil usage was really significant. The good news is my mechanic said forget about it, it would not hurt the functionality of the engine and it would keep doing that periodically.  So I ignored it as he said do and I ran it for a long time with no issues before I finally traded it in.  It did it occasionally at start up but not while driving down the road.  If when you are driving and let off the accelerator you see blue smoke it probably is more worn than what I had.  Is it using oil between changes?

 

Edited March 2, 2023 by Jworks

[richard wysong]

Probably not the valve guides if it occurs driving, more than likely something to do with the PCV system, I believe there are updated parts for that but not sure of what years it applies to

[CamGTP]

With the AFM system and PCV system on these trucks it's not uncommon for the intake manifold itself to hold a lot of oil in it. There is a small cavity in the rear of the intake manifold that can pool oil and I suppose under a very high vacuum situation that the engine can suck in a bunch of oil into a few cylinders. Then it takes time to refill that space with more oil.

 

If you pull the intake tube off and pull the throttle body off, look into the intake manifold. At the rear will be a 2-3in hole and if you stick your fingers through that and touch the bottom there is likely a pool of oil there.

 

You do kinda need smaller hands to reach back there.

[SC Dean]

Never smoke on startup. Only when the truck is well warmed up and usually at highway speeds and only when I lift off the throttle.

It does use a couple of quarts every 4K miles but it always has. I had a bad intake valve seat on the passenger side that was causing rough idle and throwing the engine light. I had the head rebuilt so that's all good but it didn't change the oil burning situation or the blue puff.

This is the second engine on the truck (don't get me started). On the first engine the oil consumption was cured (relatively) by replacing the (I believe driver's side) valve cover. But that engine never did the embarrassing blue puff.

[dna9656]

 

Drive It Forever: Your Key to Long Automobile Life

by Robert Sikorsky

 

1 quart per 1k miles can be "normal" oil consumption.According to

Drive It Forever: Your Key to Long Automobile Life

by Robert Sikorsky  Get this guy's book, it's amaze you. https://www.amazon.com/s?k=drive+it+forever+book&crid=O8IJEHNLV232&sprefix=drive+it+forever%2Caps%2C583&ref=nb_sb_ss_ts-doa-p_2_16

 

Why? Because the valve guide seals (if you have them) are designed to let some oil pass to lube the valve stems. Naturally that oil oozes on down past the stems, over the back of the valves, and into your cylinders where upon startup it gets burned and then you got your standard blue smoke on start up. Imagine that.

[SC Dean]

Once again, never at startup. Only when fully warm, and usually at highway speeds, lifting off the throttle. Happens only once every several weeks.