I just spent $140 for 3 oil filters and 4 gallons of Honda Marine oil for my 2 outboards and 12.5Kw Westerbeke. The outboard’s manual says to use oil with API Service Category of “SG” or “SH”. At Wal-Mart, the only API Service Category I could find was “SN”. I’m not sure the difference between the API ratings, so I bit the bullet and just bought the Honda Marine Oil for $25 a gallon. I was surprised to find out this stuff isn’t even synthetic! Crazy thing is, I could do a Mobile 1 full synthetic change for the same price, but it would be the “SN” API and not the “SG” or “SH”.

What’s the difference between these API Categories and would it really matter if I used the Honda stuff or the Mobile 1 synthetic?

Most of you have marinized auto motors in your boats. Do your motors also call out a special API rated oil?