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Oil change

I changed the oil in a gasoline V-6 4.3 l Chevy engine in my boat, but accidently used Shell Rotella T oil recommended for dissel engines. The engine manual calls for 40w oil, and the oil I used is 15/40w. Are there any reasons why I should be concerned?

Yes, if it calls for straight 40 weight oil, you should not use multi weight or you will cause a lot of wear. The multi weight should leak from every seal. Engines calling for 40 weight do not like thinner oils.

Agree you should change it, but your engine will not fall apart right away. Marine engines are usually run at full throttle, and 15W40 oil will cause more oil consumption than straight 40. Most 15W40 oils are rated for both diesel and gasoline engines for automotive transport use, but the full throttle marine operation requires straight 40. Diesel locomotives use this same straight 40 oil, since they have few startups and mostly run at full throttle once underway.