I have a 2013 Jetta TDI, and was using Rotella T6 since I bought it. I was always topping
off the oil, I drive 450+ miles a day, 4-days a week. I installed a catch can on the CCV
and it would fill up, so I know where the oil was going. If I was hard on it, it would fill
up twice between oil changes, but was always full at 8000 miles regardless.

Rotella T6 is 5W40.

I switched to Delo400 5W40, and the catch can NEVER fills up, and I don't have to top off
between oil changes, but if I am hard on it, maybe a half quart, and that's almost at the
10000 mark, I go 12000+, as I am changing the oil every 6-7 weeks.

Yes, I went back to Rotella T6 as a test, and the catch filled up again.

Just an observation...