It looks like you're new here. If you want to get involved, click one of these buttons!
@gtyee I like your extended week-end idea! I've been retired since 2006 so I know what a loooong weekend feels like, LOL
The oil in your 350 Mags as changed by me from Mercruiser factory break-in oil to full synthetic oil and HE (high efficiency) filters at 20 hours. The engine break-in RPM bands were strictly followed as per the manual and Mercruiser's instructions - I spoke with them many times at length regarding break-in and rpm band cruising during break-in.
Mercury PN for their HE filters is 35-892665
The oil filters were changed again at 40 hours and the oil "topped-up".
The oil and filters were changed to Mercruiser Semi Synthetic and HE filters at 60 hours. The change to semi-synthetic came after Mercruiser factory technicians said it was specially formulated to extend the life of their catalytic converter "bricks". Both oils were the same price so it wasn't that they wanted more money for an oil IMO.
BTW I was told the same thing by the guys at Mercury Racing when I went to do the first oil change for my 502s.
You may also wish to know that those 350s never burned a drop - well anything noticeable - in the way of oil during break-in or after. They are IMO the absolute perfect match for that boat.
'cause your boat isn't worth 75G LOL