During the first introduction to our 320DA I’ve checked the engines oil and noticed that it’s was dirty (black), but the it didn’t feel like it lost it’s quality, just the color. I’ve seeing oil in this condition few times in cars and simply changing the oil with filter fixes most of the discoloration. So, when we purchased the boat I’ve changed the oil and installed performance (larger) filters. After that I ran the engines for about 10 minutes and when I checked the oil I was very surprised to see that the color didn’t become any lighter. So, I got few question: What would make the oil get so dark other than not changing it on time? What would be the best way to restore the clean color? I’m thinking that it would take about 3 (2 to flush and 1 final) additional oil changes, which is about 11 4gal. bottles to do both engines. Would anyone any other than Quicksilver SAE 25W-40 (based on the manual this is recommended oil) just for flushing it or should I just eat the cost of over $200? Would I have to change the filter again, or by flushing it with new oil will keep the filter clean? So far, my plan is to drain current oil (leaving new performance filter unchanged with the assumption that it’ll get cleaned with every fresh oil I put in), refill and run the engines for 5-10 min. Then repeat the same steps until the oil is clean (hopefully, no more than 3 times). Does it sound like proper way of handling this? P.S. When I checked generator the oil was a little dirty as well, but as soon as I changed the oil with filter and ran the genny for 10 min. the color of the new oil remained crystal clear. Thanks, Alex.