Ferrari – are your oil use results the same for both cars? Are they used basically the same, and do you and your sister have the same weight right foot? Are both used for long or short trips? How far away from the engine is the Provent mounted on each car? How many miles on each car?
This isn't a full solution, but hopefully will get us closer to figuring out oil use. Calling all tribologists, chemists, and diesel emissions experts!
Volatility measures the oil that changes state - like from liquid to vapor. Noack or Din volatility will have an impact on oil consumption and viscosity change over a drain interval, but vaporized oil is sucked thru the breather, into the air intake, and burned in the combustion chamber. I’m not sure at what temperature the vapors would have to cool to in order to condense, so don’t know if this is a factor with the Provent. I suspect the stock breather plumbing is designed to keep the vapors hot enough to keep the oil from condensing.
The vent puck is also supposed to be an oil vapor separator - combining small airborne oil droplets into larger droplets and draining them back into the oil pan. I haven't seen a lot of conversation on the later models and CCV pucks - but the B4s are supposed to have the worst pucks. This liquid is what is ending up in the Provent - or being sucked into the intake and pooling in the air tubing and/or intercooler. I think it’s the liquid oil that’s combining with the soot and causing the intake clogging downstream of the EGR. I'm at 15,000 miles on the new AFL in my '97 Passat and I've used about 1/2 a quart so far - most of that after 8000 miles.
If the only oil you're loosing is coming from the air/oil separator, your oil consumption would only drop the amount you’re draining from the Provent, and it would be consistent over the drain interval.
If you’re only loosing oil due to volatility, you’d loose most of it early in the oil change interval until the lighter fractions come off in the heat. This suggests initial oil use that tapers-off off as the car is driven.
Last piece, I think, is that dirty oil gets past the piston rings easier than clean oil. This causes oil use thru blowby to start at nearly zero and increase (exponentially?) with time.
VW 505.01 doesn’t list volatility requirements. It is based on both 500.00 and 505.00. 505.00 has a volatility limit of less than or equal to 15% for 5W-40. 500.00 has a limit of less than or equal to 13%. VW 500.00 must meet ACEA A3, while 505.00 must meet B3 or B4. A3/B3 and A3/B4 both have less than or equal to 13% loss limits. It looks like 13% is the upper limit for 505.01 per VW and the ACEA.
As reported, Redline 5W-40’s volatility is 6%; AFL’s is 8.9%.
I think your oil loss is due to dirty oil getting past the rings and being burned. I don’t think you’ll notice a change in this pattern, all things being equal, by moving to oil with a different volatility, as there’s only a 4% increase available if a Group III maxes out at 13%.
Andy