1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 201Get this manual
Gear Housing Pressure Test 1Remove vent plug and install pressure test gauge
Filling Gear Housing With Lubricant
NOTE: Gear housing lubricant capacity is 22.5 floz(665.2ml)
WARNING
If gear housing is installed on engine, to avoid accidental starting, disconnect (and isolate) spark plug leads from spark plugs before working near the propeller
CAUTION