Mercury Mariner 4 and 5HP 4-Stroke Outboards Service Shop Manual 1999, Page 184Get this manual
GEAR HOUSING
Draining and Inspecting Gear Housing Lubricant
, Remove "OIL" (fill) plug (a) and "OIL LEVEL" (vent) plug (b)Let gear housing lubricant drain into clean drain pan
2Inspect lubricant for metal particlesPresence of small amount of fine particles (resembling powder) indicates normal wearPresence of larger particles or large quantity of fi ne particles indicates need for gear housing disassembly and component inspection3Note the color of lubricantWhite or cream color indicates presence of water in lubricant4Check drain pan for water separation from lubricantPresence of water in lubricant indicates the need for disassembly and inspection of oil seals, seal surfaces, O-ring s, gaskets and gear housing components