Hi all,
I switched to Rotella T6 but have a rest of Castrol 0w40 Euro formula left. I'm filled up with T6, but can I top up the T6 from time to time with a bit of the 0w40 Castrol?
This is on a BMW e46 M54B30. I am on the central OR coast, so it just gets a bit below freezing a few days in the...