Re: 1998 4.3 VOLVO. Synthetic or regular oil.
Thanks Rick. I will have to pull the cover off the boat and get the serial number so i can download the owners manual. I doubt the po was using synthetic or he would have specified. I really believe its more important to service on time than what brand of oil you use.
It's always good to follow the Manufacturers recommendations,
What's most important however, is to ensure that you change the (engine and drive) oil at (100hrs/recommended-time etc, and/or) the end of the season, so you discover water intrusion early, and fresh clean oil sits "in there" for the "long" layup.
And although you do not have a catalyst engine, for others with newer cat-converter equipped engines, be absolutely sure to use the "type" of oil recommended for those engines.
I would be willing to BET that Mercruiser or Volvo would verify a cat-converter failure before replacing one under warranty.
When they cut a failed one open, they'll be able to tell what poisoned the catalyst. (AND the wrong oil might just cause failure well after a warranty expired) [you don't want to know what they would cost!
]