Mystery Oil Loss - Where is the oil going? 2008 Yukon Denali

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Gildan

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so details on this oil. are you filling it back up every time you find it a qt low?

what if you don't fill it, will it come back up after a day of driving and be lower again in the morning? Other members have filled the kids can full and very short mileage until they replace the valve cover and soak the Rings. Around town actually makes sense to use more oil because vacuum through the PVC system is much higher under decell than it is just cruising down the highway


first thing, change that valve cover. it fixes almost everyone's oil use and I might be reading your post wrong but I'm not sure you understand a catch can fully. you don't block anything off to add it and you definitely don't have one stock in the intake. tree huggers do not care if you have a catch can lol. nothing is vented.
Interesting points. The oil level drops over night by a quart while the vehicle is sitting. Let me do a deeper dive into the phenomenon.

I drove from North Carolina to my new house in Arkansas while pulling a trailer using the trailer/tow mode as per the owner's manual. This alone would normally result in a bit of oil consumption due to the increased RPMs overall and especially due to the automatic downshifting on inclines and for engine breaking (This, under normal conditions could account for oil consumption for a number of reasons). Over 650 miles of the total distance, I didn't lose a drop of oil. I parked the vehicle, waited half an hour and checked the oil level (I check the oil level every time I stop for fuel anyway) and the oil level was spot on to the full line. In the morning I checked it again and low and behold, it was a quart low. There was no oil under the vehicle nor any on the undercarriage to be found, yet a quart vanished.

I topped the oil off to the full line, drove the vehicle about 30 miles (with the trailer), parked it again at the house, checked the oil and it was spot on full. The next morning it was yet again a quart low. Topped it again and drove about 30 miles on my way back to North Carolina, checked the oil and it was fine. I stopped for lunch, came out and checked it again before setting out and SOB, it was a quart low with no oil on the ground or leaks to be found. I topped the oil, drove the last 600 miles and arrived in North Carolina, checked the oil level and it didn't lose a drop. Drove around for two days (about 100 miles) with no oil loss. Parked the car on the second day in the garage in NC, checked the oil in the morning and SOB, it was a quart low in the morning without any oil under the vehicle or any detectable leaks. A quart of oil simply vanished without any trace or cause while sitting in the garage over night. Topped it in the morning, and two days later checking the oil twice par day, a quart vanished over night while parked. Then another two days without an issue and BAM, a quart vanished over night while the vehicle was sitting, again without any puddles under the vehicle or any signs of a leak anywhere (I used a florescent dye in the oil just to make sure there was no leaks and there were no leaks).

That said, on the big plastic intake snorkel there is a what is tantamount to a catch can near the Helmholtz resonator, but it is dry as a bone.

Just an a diagnostic wild arse guess test about an hour ago, I tried an interesting experiment involving the PCV method used on this particular 6.2L (which has a tube with an orifice on it for the PCV but no PCV valve, per se). I pulled the valve cover with the integral PCV orifice and flushed it out with a proper solvent, replaced the valve cover with a new gasket and something very odd happened - my oil pressure went up by abut 5 to 10 PSI all around. I parked the Puke in the garage and checked the oil level after the oil settled for half an hour and it was spot on full. An hour later, a quart was suddenly gone with no oil on the ground and no leaks whatsoever. The oil seems to vanish while the vehicle is sitting still in the garage. And no one can figure it out because unless there's a glitch in the matrix, the oil is simply vanishing into a black hole (and this was after a 20 mile trip for test purposes). If I was losing a quart of oil out the tailpipe in 20 miles I'd have a cloud of blue smoke behind me that would be visible from outer space.

Unless there is something severely odd about the vapor pressure characteristics of the oil or the laws of physics, there is absolutely no explanation of why this is happening.
 

swathdiver

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I think your rat found his way into my garage. My daughter grabbed a bottle of oil off the shelf the other day and oil spilled all over her leg and onto the floor. The cap was tight, when she turned the bottle around, we could see where a rat had eaten through the 1 gallon bottle exposing the oil. Or maybe there's two of them!

My transmissions are also in front of 3.42s and don't hunt for gears while towing. Tow/Haul provides no benefit unless your GCW is over 10,500 pounds.
 

rdezs

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A couple noteworthy points.....

1. Your fuel mileage, while much better than average, could be a symptom. Such as.... You have additional fuel entering the cylinder. Oil. Theoretically, if it's entering as a mist, it is possible it's burning fairly clean..... But that clearly doesn't address oil disappearing overnight. And if it is going out the tailpipe, most people would be in agreement that your catalytic converters are not long for this world. But let's not forget there's many diesel pickups out there with catalytic converters..... I have a Ford 6.0 powerstroke that came with one.

2. Time to get an oil analysis done. It might be useful to see what actually is in your crankcase.

3. If your oil is extremely aerated, and full of air bubbles... And sits overnight.... Yes, the oil level will drop much like a glass of beer with foam on top. But... I would expect your oil level, for example after driving in town for an hour, to be a quart high on the dipstick.

4. At this point I would dump the oil and filter and take a sample after a brisk 20 minute drive around town. Catch some in a glass jar and take a close look at it for trapped air bubbles. Mark a line with a sharpie at the oil level in the glass jar and let it sit overnight. While awaiting the oil sample results, I'd put some 10W-40 in and see if the symptoms change.

5. Oil aeration is not uncommon in LS engines. Besides oil being whipped up around the windage tray, the oil being released from the pumps pressure relief valve becomes very aerated. Anti foaming additives in motor oil are supposed to address this. So as a test of sorts, I would switch to something like the Valvoline synthetic high mileage motor oil. (Which raises the question, exactly what oil is in the pan and what oil are you adding?) And yes, extremely aerated oil will create more vapor in the engine and be sucked through the PCV system to be burned.

My best speculation is the root cause may in fact be the oil pump itself, possibly in conjunction with the oil you are using and it's inability to control foaming. You also mentioned the mechanic change the o-ring on the pickup tube. If he used the wrong o-ring, the smaller one or got it in there wrong, sucking a little bit of air and will also aerate it inside the pump.

That's about all I can think about on this.....
 

B-train

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This is good information.

After reading through all this, here's my thoughts.

1. Checking hot will have a higher level as all things expand when hot. This would explain why it appears lower when it cools off.
2. @rdezs has a good speculation on the oil getting whipped up. Is it possible that you keep adding an extra quart that gets whipped up and consumed due to being overfull?
3. I'd drain the oil when hot. Refill with 6 quarts of 5w-30 and a new filter of the correct size. Your level should be spot on the Full mark.
4. If it changes overnight, then you must have an oil gremlin.....
 

donjetman

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@Gildan
GM TSB 10-06-01-008M
https://www.tsbsearch.com/GMC/10-06-01-008M
includes:
driver side valve cover GM# 12570427, same as Dorman# 264-965
pressure relief valve deflector GM# 12639759
piston/combustion chamber soak

Prior to doing this TSB, many of us have installed a catch can to verify the oil was being sucked out thru that path:
https://www.tahoeyukonforum.com/threads/get-a-catch-can-before-any-mods.49716/page-53#post-1288561

Hundreds of folks at this forum have had this problem, myself included :(
 

j91z28d1

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just to add while the air intake is technically part of the pvc system. but It's not the part where you usually see oil. you'd basically have to be doing track days or have a cracked ring land to blow oil back up the clean side air intake. the oil gets sucked in to burn from the drivers side valve cover. hince the updated part number with working oil baffles in it


I feel rdezs is on to something with the foaming oil, you're using what is a fairly normal amount of oil for that old style valve cover but it's not showing up on you dip stick till it sits long enough.

that's all that makes sense short of a glitch in The Matrix.


what is you oil pressure out of curiosity?
 

Fless

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That said, on the big plastic intake snorkel there is a what is tantamount to a catch can near the Helmholtz resonator, but it is dry as a bone.

What does this catch can looking thing look like?; post a pic of it.

Any chance you took a pic of the underside of the driver's side valve cover when you had it off? If so, please share.
 
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