The common practice is to change when winterizing, I have always differed from the crowd, I like to check the dipstick & "read" the oil in the fall when putting the boat to bed for the winter, smell for gasoline, milkyness etc. if present I address right away. If normal just dark in color I wait until spring, & allow any condensation that might form drip into the old oil, then BEFORE starting for the first time in the spring drain the old out completely & replace with new oil, filter, & trans oil...works for me.
