Well i am not sure with Amsoil products but I was using a fully synthetic organic ester for 130000 km with a 25000 service interval but every 10000 I do change oil filter and top up. Engine was great but didn't eat engine oil but when i opened up the engine and it was all black underneath. Massive carbon build up, It's not a problem with the oil, I suspect the problem is between the inefficient campro engine and sub par proton and Bosch oil filters. Maybe a ultrafiltration filter would be better but I've decided not to take the risk anymore and go back to a 10k service interval. Wonder what efficiency oil filters does Amsoil have? Hmm.....