Most newer boat engines and outboard motors come with oil injection systems, but older models will not. When using an older model of boat engine or outboard motor, it’s often necessary to premix your gasoline and outboard motor oil. Finding the correct gasoline to oil ratio is important, but it’s also important to use the right oil. When it comes to older boat engines and motors, most any TC-W3 certified oil will do. Manufacturers will tell you that you need a specific oil, but this is more an attempt to encourage the purchase of their products than an actual necessity.
Manufacturer branded oil contains special additives, and when purchasing a new boat engine or outboard motor, it’s a good idea to use the manufacturer branded oil to increase its longevity. But with older engines and motors, you can’t expect to prolong their lifetime by a whole lot purchasing expensive oil. In general, you can just buy generic TC-W3 certified bulk outboard motor oil from a retail supplier and it will work fine.