I have twin low hour 4.3l (chevy) Vortec TBI engines in my 27' Four Winns. This season I accumulated only 30 hours on the engines (normal season is 50-75 hours). I did not change anything this season regarding using my engines differently, aside from buying a house which took most of my summer with painting, remodeling, etc. so I ended up boating a lot less. I wasnt going to change the engine oil for the winter - I ALWAYS do, but with only 30 hours, I figured I could wait until spring. I mean, after all, every time I change the oil - even with 50+ hours on it, it comes out translucent still. Might be brown, but its not BLOWN OUT dark brown. Yesterday when I winterized the boat, I noticed the starboard engine - which is my "good" engine, oil was very dirty. I was very surprised with such low hours on that OCI. Not to mention the engines low relative hours, and that Ive basically had them since new "over" maintaining them. My port side engine, which Ive had problems with in the past, my "misbehaving" engine, lol, was much cleaner than the starboard. I had Rotella T5 10w-30 in the sump (semi-syn) and used Purolator oil filters. It was my first season with that oil. I had previously used Rotella T or Delvac 15w40. Both engines are good on their tune ups, I use the proper gasoline and there are no driveability/performance problems to note. I cant seem to grasp why my starboard engines oil was so black, and my port wasnt. It never did this with the Delvac or Rotella T 15w40.... Discussion?