2009 Yamaha F40 Outboard Service Manual, Page 352Get this manual
Predelivery check
Checking the engine oil level
1Put the outboard motor in an upright positionNOTICE: If the motor is not level, the oil level indicated on the dipstick may not be accurate2Start the engine and warm it up for 510 minutes3Stop the engine and leave it at "OFF" for 510 minutes4Remove the top cowling5Remove the dipstick and wipe it clean with rag6Insert the dipstick completely for accurate measurement and remove it again7Check the oil level using the dipstick to make sure the level falls at the center between the upper level and the lower level bFill with oil if it is below the lower level b, or extract to the center level if it is above the upper level a