A3/B4 and C3 oils

Mar 9, 2021
Can I mix oils with different ACEA specifications, specifically a3/b4 and c3 oil?
mixing a C3 with A3/B4 will thin out the additive package - other than that there's no reason why you couldn't. Oils nowadays are mixable.
myself I have mixed 95% C3 oil with 5% HDEO (Delvac MX15W40) to bring up the additive levels a notch.

No side effects during that OCI.

Think of it like this: You go on a trip, have top stop for gas and then you see your oil level is low. But the choice is limited at the rural gas station. Mixing whatever they have is better than risking a oil level too low.
well he hasnt told us what he is planning .... maybe he has a leftover quart of C3 oil and wants to use it?
That's exactly why I asked this. I have a liter of C3 oil that's left from my other car oil change.