Excessive oil usage through intake

[Sparky]

My coworker has a 2007 Trailblazer LT 4.2L with 251k miles. She said recently that it has been hesitating badly when pulling away from a stop. OK, clean the throttle body, I've been down that road before.

Now the thing is she said oil consumption has gone way up recently where she's having to add a quart of oil between changes, and she still does the every 3-5k miles with conventional (at the dealer). When I pulled the intake resonator the little L shaped hose that connects to the top of the valve cover was covered in oil. It is also cracked a bit, so it should be replaced. But that intake resonator was loaded with tons of oily goo, enough that I was actually dumping it out.

We went ahead and cleaned the throttle body and it is running great again. That said, something has to be causing that much oil to be getting sucked through the intake that badly. My old 2002 with 215k miles never had enough oil in the resonator to actually flow or pool anywhere, just had a oily film coating inside.

What could be a cause of this much oil in the PCV? I'm thinking possibly excessive blowby from worn rings, but maybe something else I'm not thinking of.

 

[littleblazer]

I would have to say blow by as well.... maybe it get over filled and foams? The crankcase is some how being pressurized though. Bad pcv... I forget if it lets pressure out or what... I just don't remember. If it's stuck closed maybe.

 

[Sparky]

Pretty sure the i6 doesn't have a real PCV valve though, just a breather tube to the intake.

 

[mrrsm]

This is a rare phenomena in modern engines...but "Back in The Good Ol' Days"... (silly expression) prior to the introduction of Oil Pan baffles and "Anti-Aeration Plates"... in engine where the Oil Level was WAY OVER-FILLED.... it was possible for the Crank Throws and Counterweights to dip down into the Oil in the Pan and Whip it Up into a kind of Brown, Foamy Meringue Fluffed Up Semi-Solid that could wind up aerating almost the entire contents of the Oil Pan... sufficient to cause Oil Pump Cavitation and Engine Failure from Oil Starvation.

As first suggested by @littleblazer ... If the Oil Level is Too High in that engine and this "Whipping Action" is possibly involved... that Brown Foamy Mass could quickly rise just like an Angel's Food Cake Batter Mix to the top of the inner engine spaces and then easily get sucked inside that Little Elbow and vacuumed further up inside the Intake Manifold.

 

[Sparky]

Well it wasn't overfilled because it was down by almost 2 quarts in 3k miles - yeah ouch, I had it wrong how much it had used recently.

 

[littleblazer]

I vote blow by then, I'm not sure if a compression test will show it... I don't know if it is possible but check the pcv and see if its constant or pulsing. it's unlikely all the cylinders have equal blowby.

 

[mrrsm]

Yes... but think about it... @Sparky ... imagine how quickly this action can occur at 2,000 RPM ... and once the Oil Level drops in the Pan below the reach of the contact points with the Rotating Assembly... it would subside... so more than likely... the oil was that moved up into the Intake Manifold would distribute itself inside there like a Gooey Mass and adhere to the inner surfaces all over fairly well...pooling in any spaces large enough to capture the lubricant... So your observation of Rapid Oil Consumption makes perfect sense.

 

[Sparky]

Well, we cleaned it out and the level is proper right now, so guess we'll see what happens. But I do suspect she's just running into worn engine symptoms. I know Regulator's Envoy had started drinking oil pretty good sometime after the 250k mark for example (I think he got to around 300k before it blew up).

 

[littleblazer]

Well... that happened in the escalade once.... we took it on a 250 mile trip and got the oil changed the night before. the next morning there was a puddle the size of the truck and then some in the driveway. and the damn thing was still at least 2 quarts over. I could see it... but I wouldn't think it run itself down below normal levels...

 

[mrrsm]

Just a thought about this from another angle. For the sake of the argument... if the Engine Oil was initially over-filled and then this "Phoaming Phenomena" happened in the same manner that Beaten Egg Whites remain solidly filled with air bubbles... after a reasonable steady drive time, the Foamy Oil might have risen substantially up taking up the space inside of the Crankcase and yet... NOT be registering its presence on the Dip Stick when checked soon afterwards..... and you'd never know that the Oil was still in there... but in an altered state that prevented it being part of the normal Liquid Oiling System.

But after having enough time for the Air Bubbles to settle out... The reconstituted Solid Foamy Liquid would then have the chance to drain back down inside of the Crankcase and be added to whatever the contents of the Oil Pan were. So ... If any New Oil was added prior to this "rest-then-drain period"... the Crankcase would certainly be fuller afterwards.

 

[Sparky]

I would think after 3k miles it would have had plenty of time to run down.

 

[m.mcmillen]

A compression check probably would not show anything. A leak down tester is what you need to check for worn out rings. Basically, you use compressed air and there are gauges on the tool that will tell you how much pressure the cylinder is holding. Some leakdown is normal but if there is a lot, that will be where your consumption is coming from.

This wonderful ethanol also makes the insides carbon up pretty bad. You could have a stuck oil ring.

 

[HARDTRAILZ]

I am thinking some ring wear