Oil is the life blood of any engine. That's why it's important to drain and replace oil whenever your boat will be unused for a significant period of time, particularly at the start and end of each boating season. Check your engine manual for recommendations on how often to change oil based on hours of operation, but always remember it's even more important to change oil when your boat is not in use to avoid acid and moisture from damaging engine parts.
Fresh oil extends the life of your engine, plain and simple.
The video above and the notes below are specific to changing oil on a Mercury brand 40-60hp four-stroke motor. Many of the principles are the same for other motors, but it's recommended to seek out the proper instructions for your specific engine.
Before changing oil, it's a good idea to run the engine a few minutes to let the oil warm up and flow, allowing any contaminates to move from the bottom of the pan. Let the engine cool before changing the oil, so you don't burn yourself on it.
To find out more information on changing engine oil on Mercury outboards, refer to a Mercury owners manual or visit mercurymarine.com.