Yamaha F100B F100C Outboards Factory Service Manual, Page 58Get this manual
Periodic checks and adjustments
NOTE: Change the oil if it appears milky or black If the engine oil is above the maximum level mark a, drain sufficient oil until the level is between and If the engine oil is below the minimum level mark b, add sufficient oil until the level is between and b
Changing the engine oil
1Remove the engine oil dipstick and oil filler cap 1
NOTE: Be sure not to spill any fuel when removing the fuel filter cupS60C3060