[Junkyard Dog]

My Yukon has huge billows of smoke on startup, leaving black residue in the tailpipe and burning through a lot of oil. It goes away about a quarter mile down the street, and, if the engine is hot on a restart, such as after a short stop to get gas, there is no smoke on restart. If the engine gets cold (even a little), then the huge billow of smoke pours out of the exhaust again.

The funny thing is that it did this last year when the weather was cold, too. When the weather warmed up, this weird symptom went away. No smoke. No oil consumption.

I had thought the engine (valveguides or something) was just worn out (high mileage), but the symptom completely disappeared.

Now it is back!

Any thoughts as to what this might be? I know a lot of people here drive GMC Yukons and Chevrolet Tahoes.

This has to be clogging up the catalytic converter and can't be good for the engine internals.

Oh, one more symptom - sometimes it has pinging (detonation) which I take to be from oil in the cylinder. This also happened last year and disappeared with the smoke when the weather turned warmer.

Help!

[Sirrotica]

Members helping members would be a better choice to post this in, however I assume your PCV system is having a hard time dropping all the oil out of the crankcase vapors and it is pulling oil into the intake tract causing this problem. If your engine is an LS series (you don't mention what engine in the post) it's a fairly common problem and is remedied by an aftermarket oil separator vessel inline in the PCV plumbing trapping the oil before it can get into the intake.

One symptom your describing is the detonation which is caused by excessive carbon deposits on top of the piston and in the combustion chamber which raises the compression as well as causing red hot carbon spots which will cause premature detonation, or knock. Running GM TEC (top engine cleaner) or even running some water through the engine will help get rid of excessive carbon deposits.

The smoke at startup after sitting overnight may be valve seals or excessive stem to guide clearance so you could have 2 separate problems to correct. Hope this gets you looking in the proper areas to remedy the problems.

[Junkyard Dog]

Originally Posted by Sirrotica

Members helping members would be a better choice to post this in

Sorry. I thought about that, but the description did not seem to fit this thread.

however I assume your PCV system is having a hard time dropping all the oil out of the crankcase vapors and it is pulling oil into the intake tract causing this problem. If your engine is an LS series (you don't mention what engine in the post)

It is a 4.8 liter V8 - I am embarrassed to say I do not know if that is an LS series.

it's a fairly common problem and is remedied by an aftermarket oil separator vessel inline in the PCV plumbing trapping the oil before it can get into the intake.

I will research this.

One symptom your describing is the detonation which is caused by excessive carbon deposits on top of the piston and in the combustion chamber which raises the compression as well as causing red hot carbon spots which will cause premature detonation, or knock. Running GM TEC (top engine cleaner) or even running some water through the engine will help get rid of excessive carbon deposits.

Except that this happened before and went away and the detonation went away, too. It is no use putting a cleaner in there when the engine is dumping massive amounts of oil into the combustion chamber.

The smoke at startup after sitting overnight may be valve seals or excessive stem to guide clearance so you could have 2 separate problems to correct. Hope this gets you looking in the proper areas to remedy the problems.

I thought about the valve seals and guides last time this happened, but, like I said, the problem went away on its own for 8 months now, and it only returned with the cold weather.

[SavingTheBird76]

Time for a valve job...runs about $600 to rebuild a set of heads..if you do the labor to remove them and strip them down.
Did you use thicker oil for the summer?
Cold temps and thin oil and worn valve stem seals is my guess.

[Sirrotica]

Good thread here about reasons and in post #20 it tells the GM service technicians procedure to narrow down the causes of excessive oil consumption:

http://www.fullsizechevy.com/forum/g...rra-5-3-a.html

and another:http://www.gm-trucks.com/forums/inde...owtopic=117624

[Junkyard Dog]

Thanks, Sirrotica!

From your first link.

the fixed orifice PCV and baffles in the LH valve cover were all plugged up, so it was essentially siphoning oil into the intake. It then promptly burnt it off during startup with a nice blue cloud.

I talked to a GM service guy last night (just met him by chance) and this is exactly what he told me is a common issue.

[Junkyard Dog]

UPDATE: This is precisely what it turned out to be. I removed the coil packs and valve covers and cleaned out the PCV orifice and fresh air tube using Seafoam and an air compressor, sprayed the rest of the Seafoam into the intake with the engine running, and it has not smoked or used any oil since!

[Sirrotica]