How Important Is Changing Engine Oil?
By Don Casey
Revised by BoatUS editors in April 2012
Not only does the grit in dirty oil wear precision surfaces, but the acids that contaminated oil invariably contain are dissolving internal engine parts while the boat is sitting idle. Frequent oil changes ward off breakdowns and extend the life of your engine(s) by thousands of hours--simple as that. Engine manuals typically specify changing the oil every 100*, 125*, or 150* hours. Pay attention to that asterisk. It means "but no less than once a year." If your boating is seasonal, once a year is not often enough. Change the oil when you commission your boat in the spring and when you winterize it in the fall. You will never get a better return on a $40 investment than from changing your oil twice a year or every 100 hours.
Running the engine is always a prerequisite to an oil change. You want the oil warm enough to flow freely, and you want the contaminants in the oil, not lying in the bottom of the pan. Drain the oil cold and a lot of the contamination stays behind. Because a quality oil filter should be good for 200 to 300 hours of running time, engine manufacturers sometimes specify a filter change with every other oil change. The problem is that filters harbor a significant amount of oil. Not changing the filter is a bit like pouring this morning's coffee over an inch of yesterday's coffee remaining in the cup. When you change the oil, change the filter.