[recppd]

I recently (June 2018) purchased a 2000 Tiara 3500 Open with twin Crusader 7.4L MPI engines. They run great, but I had no idea what was in them for oil since the owner always had a local marine mechanic do all his work. I called the mechanic today and he told me he used Mercruiser Synthetic 25w40 in the engines. Does this seem right? The manual calls for 15w40 and when I looked up the oil he stated it says its for an outboard engine. The boat is in Massachusetts so not super hot temps, and the boat will stay in during the water until probably late September to mid-October. Any thoughts?