1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 228Get this manual
Bleeding Air From Power Trim System To determine if the Power Trim system contains air, position engine so two trim rods are slightly extendedDo not extend tilt ramPush down on lower unitIf trim rods retract into trim cylinders more than 18I (3.2mm), it will be necessary to bleed air from the Power Trim systemBleed air from Power Trim system as follows: IMPORTANT: This trim system is pressurizedRemove fill screw only when engine is trimmed to the full "up" positionRetighten fill screw securely before trimming engine downTrim engine or times thru entire trim range; check fluid level (fill if necessary) each time engine is trimmed to the full "up" positionSee "Checking Fluid Level and Filling," preceding20319Fill Screw