Hi there, I bought a clean 2015 q7 that drives great. The engine runs well, starts right up, smooth, fast, you cant barely see exhaust fumes if at all. Nothing blue or excessive. There is no evidence of leaks in the engine bay or in the driveway.

The only issue is I lose oil about 1 quart per 500-750 miles. The PVC valve has been changed. There also no codes.

What is going on here?

Thank you!

 

OK, EXACTLY what I just went through and let me tell you, get ahead of it, before you get codes and worse. I believe it was a faulty PCV that started the whole thing. And I should have had it changed. 2015 with 172,000, but burning oil for a few K. I would definitely have that changed.

AND I would highly recommend purchasing Ross-Tech VCDS software and read the codes, any stored or erased.

RINGS: The oil disappearing trick that Audi claims is completely normal because "the oil sprays into the turbo and burns up". WTAF did they say?

This is what I learned the hard way, after a miserable misfire and #5 cylinder shutting down
OIL consumption: Purchase 2 cans of Berrymans B12 chemtool. Remove coil packs and spark plugs and pour the chem tool into each cylinder. (You can find many youtibe videos on how to)
You will turn the motor by hand every, like 6 hours in a 24 hour period.
Remove the fluid from cylinders. Now, I did this by placing a towels over the valve covers and cycling the starter/engine several times. My thoughts for doing it this way? To spray the chemtool into the valves. and let it sit for another day to help eat the carbon build up off the valves.
This will clean the tops of the sticky rings that are allowing the oil to blow by as well as raise your compression.

Next, Oil flush: I used EPR and did the flush twice before changing, letting sit a day in between each session. (again, youtube videos available)
You can find my post with updates in here: Zero Compression , But there are many threads with same type of situation.
I just got mine back after a fresh rebuild and its running great.

 

With 175k miles on the clock it could certainly be a mixture of things allowing oil to be consumed by the engine, like valve-guide seals leaking, etc., but what the 3.0T engine is famous for is the low-tension piston rings getting carbon-captured from extended oil change intervals coupled with meh fuel quality. As it gets worse, the oil consumption goes up-up-up! Owners who use 5k miles to 6500 miles OCI generally have no issues with oil consumption when they begin that regimen prior to the onset of rings capture occurring.

Since your oil use in severe, the best way to fix is reference to the piston soak threads or go online and look that up...there's a defined process to do it correctly. There's also products out there specifically designed for carbon-captured rings to be run in the oil to deal with cleaning/releasing the rings that way, since there's a fair bit of oil making it past the rings to carry the solution with it, but that costs more, although it's simpler procedure. You got options, but definitely strike while the iron's hot before you lose a valve, as the prior member did.

 

Thank you.

 

If you want to validate the before & after, then do/get a compression check/test on all cylinders before & after so you have a baseline of the compression loss, etc. Other known issues is carbon build-up on the intake valves related to it being an early-ish DI engine design (no port injection used), and that'll bith you in the butt too. Carboned-up valves are 'managed' via walnut blasting the valves to remove the build up.

4L Q7 is a great platform, regardless of engine, but has a fair few known issues to look out for, so be sure to spend a few minutes watching videos or articles about buying a used Q7 to understand the common problem areas. Same goes for engines. The learning curve is steep, but totally worth it.

 

Also, I can't underestimate looking for other places the oil is leaking.
On my 3.0T, one location I found was the Accessory Belt Idler. Turns out, its oil cooled, so there was a substantial amount of oil build up behind it on the block. After replacing it, the oil consumption went down noticeably.

 

What are the best additives I can add to the oil to clean up the piston rings? Thank you!!

 

I have sifted through 1000s of posts and videos, experiments and scientific studies, and endless hours of research, conclusion: the best of the solutions I chose are what I listed prior, Berrymans B12 and EPR oil flush. 1 might work for some and the other of the rest, I used both, then changed the oil. I am currently using Valvoline Restore and protect 10W-30 for many reasons and BMW recommends it.
I can say from my own experience now.
This process did raise my compression up from around 90 to 150ish, unfortunately, I found a broken valve in #5, which I just had replaced. So that tells me it cleaned the rings at the least, maybe some valve also.
All pistons were at 150 prior to having the motor gone through due to broken valve and they are now sitting at 160 after a valve seating/grinding.
A soak and flush are the cheapest route to discovery of it being rings. And again, the PCV is also a known issue for creating the problem of oil burn. I used 1 quart/ 10K until I had the PCV changed, due to coolant leak. After that? 1 quart/7-800 miles.
As prior mentioned by '10 and my friend Mike, who also lurks here and helped me greatly, build the baseline with compression test first, then you know exactly what your results are!

 

And if you are looking to DIY this, you can get a cylinder compression gauge/adapters kit as a loaner tool from most chain Auto parts stores like Advance/O'Reilly/AutoZone, etc.