you've got a thru-hub exhaust if you will discover exhaust holes around the engine gearcase across the prop shaft. Non thru-hub is strong around the prop hub. Non Thru-hub Exhaust Oil & Filters: Mercury engine oil and https://cecilyyifp629590.theideasblog.com/30174090/the-smart-trick-of-yamaha-outboard-motor-deals-that-nobody-is-discussing