Engine oil Castrol or OEM Honda

I use 15w40 GTX Diesel Castrol oil, it works.

My 10k UOAs on Castrol 5w40 were just fine, but VW 504 is mid-saps so it might not have as much staying power even thought it's "better" oil.

Our Tig is coming up on it's 4th change (every 5K) and hasn't lost any significant amount between changes. So far all changes have been the 508 spec Castrol 0w20.

I really like Castrol oil. I used the VW High Performance twice, and it was fine, but I still preferred Castrol.

The approach to go with 10W40 is absolutely right - from my experience the best oil for that kind of engines! Take an expensive Castrol Magnatec Oil and it runs well.

As an aside, all the oil used to be Castrol and has now transitioned to a VW boxed product produced by Mobil 1. THAT is the correct oil.

I've switched to Castrol Magnatec 10W-40 which seem to do better wrt oil pressure.

Try using 5w30 castrol from walmart black container with green writing, since switched been driving 2.7k with in 2-3 month oil on the same level

I'm running 5qt 5W40 full synthetic oil (Castrol Edge, to be specific). The oil is changed yearly cause I never get close to the 10k miles suggested by VW for an oil interval.

I personally used to run mobil 1 0w-40. as you said its super thin and seemed to just barely get the job done. Recently switched to castrol SLX 5w-30 and I am decently pleased with the first two changes.