Oil Consumption Plan of Attack

B6/7 S4/RS4
#1

Hey all, I know this topics been beat to death but am looking for specific input if anyone wants to help :slight_smile:

2005 B6 S4, Tip. Currently at 176,XXX miles.

Recent History:

  • Did timing 7 months ago at 164,XXX miles.
  • PCV valve was changed with the timing work
  • Compression test was done at this time, everything was within roughly 135-155
  • precats were gutted at this time
  • FI catback was installed in early Sept this year

More recently (last few months I’d say) I’ve been consuming more and more oil. Just got back from a recent road trip, maybe 1500 miles total, where I consumed about 4 quarts, maybe a smidge more. Previous to the timing work I was at about 1qt every 1500-2000 miles. So something has definitely changed.

One thing I have noticed ever since getting the new exhaust catback is a lot of black residue building up on the rear bumper/trunk. Seems somewhat oily and washes off well enough with soap but doesn’t rinse off. Is that due to the catback or is it pointing to a particular type of oil consumption? My line of thought is if I am getting oil out the tailpipe it is likely cylinder walls or piston ring or valve guide seals? And not PCV?

I am wondering what steps to take to diagnose the culprit. From my research I’ve found it could be any of these or some combination of them:

  • Bad PCV
  • Scored cylinder walls
  • Bad piston rings
  • Bad valve guide seals

What tests can be done to narrow this list down?

  • A good compression test would indicate cylinder walls AND piston rings are in good shape, correct? Or is that not necessarily true?
  • Can the PCV be bad so soon? I did buy an OEM (the expensive) one since I heard the other aftermarket ones can go bad faster. Is there a good way to check the PCV or am I better off just dropping another $120 and replacing it?
  • Does a leakdown test make sense to do if the compression tests OK? What does the leakdown tell me?

Right now I am trying to prioritize my troubleshooting. So far I am thinking of:

  1. Doing a compression test
    2a) If compression tests OK, I plan to replace the PCV
    2b) If compression tests BAD, I ??? borescope? leakdown? resign myself to adding a quart and washing the rear end every weekend? car is too far along to justify an engine teardown and rebuild IMO.

You all have been very helpful in the past, so many thanks for any advice you can give!!