For years I have run a synthetic oil called Royal Purple in my Yanmar and my Westerbeke generator. The boat lives in St Martin so this involves shipping the oil to the Caribbean because you can't buy it there. I switched to Royal Purple when I learned that Houston Towing, the biggest tug operation at the Post of Houston switched to it to extend the time between oil changes. Now I have put a brand new Yanmar in the boat. The mechanic who did the repower insisted that we do the break in on Delo. He claims that Delo is better for diesel engines because it cleans better than synthetics. I am going to change to Mobile One if I stay with a synthetic oil (so I can purchase it in the islands). Anyone else want to offer an opinion between synthetic motor oil and good old Delo (Diesel Engine Lubricating Oil)? My Westerbeke manual says to change the oil every 50 hours and with the synthetic oil I have lengthened that to 200 hours. I had Royal Purple do an analysis on a sample of the used oil with 200 hours on it and they said it was still perfect.