----- Original Message ----- From: "Garrett Lambert" <e16@telus.net> > Twin Lehman 120's. The manual says change the oil every 200 hours. It was > last changed in June, about 50 operating hours ago, and the then owner > switched from regular oil to synthetic. > Hi Garrett, I agree completely with what Al Johnson said. If the manual says to change every 200 hours that should be read as "Every 200 hours or annually, whichever comes first". There are two schools of thought about annual oil changes; The first says to do so at the end of the season for all the reasons that Al gave in his post. The second says to do so at the start of the season to remove any condensation that accumulates over the off season. Of course there's also the "belt and suspenders" approach of changing oil at both ends of the season since oil is fairly cheap compared to your engine(s). IMHO changing after the season is the way to go. I don't think that synthetics make economic sense for a recreational trawler but rather than belabor that argument (in deference to those TWListees that are troubled by such things) I will refer you to the following links: http://www.samurai.com/lists/trawler-world-old/1999/01/0165.html An explanation of the differences between mineral and synthetic lubricants. http://www.samurai.com/lists/trawler-world-old/2000/04/0374.html Basically, a repost of the above link with a few added thoughts. http://www.samurai.com/lists/trawler-world-old/1999/01/0267.html Sort of a disclaimer to the first link that explains my outlook on the subject. The second link also proposes a possible explanation for Tom Clements' question about Yanmar's recommendation against synthetics. There may be other explanations, but I can't think what they may be. As to the question of synthetics leaking, there's a simpler explanation than the possibility of seal incompatibility. Synthetics tend to be thinner than mineral oils at all but the highest temperature. They can get away with that because of their inherently high viscosity index and that's one of the main reasons behind the claims of superior fuel economy with synthetic oils. The drawback to that is that it's easier for a thinner oil to leak through the tiniest of holes. As an example; When Mobil 1 was first brought to market it was a 5w20. It sold well at first but then it gained a reputation for leaking out of engines that were thought to not leak. After a few years of slumping sales Mobil 1 was reformulated as a 5w30 (slightly thicker and didn't leak out as badly). That all happened almost 20 years ago and today's engines are tighter so that the problem wouldn't be as pronounced any more. In fact there is now one grade of Mobil 1 that is classed as a 0w30 which is actually thinner than the original. BTW: Mobil 1 is not recommended for heavy duty diesel service. Speaking of recommendations. Bob Smith of American Diesel recommends a straight 30 weight oil for Lehman engines while the heavy duty synthetics that I'm familiar with are all multigrade products; Mobil Delvac 1 is a 5w40, Exxon XD3 Elite (blend) is a 10w30 or 15w40, and Chevron Delo 400 Synthetic is 0w30 or 5w40. While I don't agree with Mr. Smith on this there is no disputing his knowledge of Lehman engines - Food for thought. Hungrily yours, Alex

-snip- The second says to do so at the start of the season to remove any condensation that accumulates over the off season. Of course there's also the "belt and suspenders" approach of changing oil at both ends of the season since oil is fairly cheap compared to your engine(s). IMHO changing after the season is the way to go. -snip- Put my vote (mind the Chad!) on the side of spring AND fall for the reasons noted. Changing oil is cheap and easy, which, by the way, is a better description of me than "belt and suspenders." Todd Mains M/V Pingino Portland, Oregon