Yamaha F100B F100C Outboards Factory Service Manual, Page 66Get this manual
Periodic checks and adjustments
2Place drain pan under the drain screw 1, remove the drain screw, then the check screw to drain the oil
4Install the reservoir cap, and then tighten it to the specified torqueReservoir cap: Nm (0.7 kgfm, 5.1 ftlb)
Lower unit
Checking the gear oil level
1Fully tilt the outboard motor down
2Remove the check screw 1, and then check the gear oil level in the lower case
NOTE: If the oil is at the correct level, the oil should overflow out of the check hole when the check screw is removed3If necessary, add sufficient gear oil of the recommended type until it overflows out of the check holeRecommended gear oil: Hypoid gear oil SAE: 90 4Install the check screw, and then tighten it to the specified torqueCheck screw: Nm (0.7 kgfm, 5.1 ftlb)