1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 178Get this manual
2Place block of wood, as shown, to prevent propeller from rotating and to protect hands during removal of nut3Remove nut and pull components from shaft51552Oil Level ScrewFillDrain ScrewVent Screw
19183Block of Wood
2Inspect gear lubricant for metal particles (lubricant will have "metal flake" appearance)Presence of fine metal particles (resembling powder) on the drain plug bar magnet indicates normal wearThe presence of metal chips on the drain plug bar magnet indicates the need for gear housing disassembly and component inspection3Note color of gear lubricantWhite or cream color MAY indicate presence of water in lubricantGear lubricant which has been drained from gear case recently in operation will have yellowish color due to lubricant agitationaerationGear lube which is mixed with assembly lubricant (Special Lube 101 or 2-4-C wTeflon will also be creamy white in colorThis is normal and should not be confused with the presence of waterIf water is supected to be present in gearcase, pressure check of gearcase should be made (with no lubricant in gearcase)Gearcase should hold 10 to 12 psi of pressure for minutes without leaking downPouring portion of the gear lubricant into glass jar and allowing the lubricant to settle will allow any water in the lube to separate and settle to the bottom of the jar4Presence of water in gear lubricant indicates the need for disassembly and inspection of oil seals, seal surfaces, O-rings, water pump gaskets as well as gear housing components for damageIf gearcase is rebuilt, gearcase should be pressure checked before filling with lubricant