Mercury Mariner 25HP 4-Stroke Outboard Service Manual 1997, Page 273Get this manual
Gear Housing Pressure Test 1Remove vent plug and install pressure test gaugeTighten securely_
Gear Housing Installation
Filling Gear Housing with Lubricant
NOTE: Gear housing lubricant capacity is approximately 14.9 floz(440 ml)
If gear housing is installed on outboard, disconnect (and isolate) spark plug leads from spark plugs before working near the propeller
CAUTION
Do not use automotive grease in the gear housingUse only Quicksilver Gear Lube1Remove any gasket material from "Fill" and "Vent" plugs and gear housingInstall new gaskets on "Fill" and "Vent" plugs2Pressurize housing to 10-1 p.s.iand observe gauge for minutes3Rotate drive shaft, prop shaft and move shift rod while housing is pressurized to check for leaks
IMPORTANT: Never add lubricant without removingVent" plugGear housing cannot be filled because of trapped airFill gear housing when driveshaft is in vertical position2Remove "Fill" plug and gasket (a)