1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 10Get this manual
Checking Trim System Fluid Level IMPORTANT: This trim system is pressurizedRemove fill screw (b) when outboard is trimmed to the full "up" positionRetighten fill screw securely1Trim outboard to full "up" positionEngage tilt lock leverTrim system fluid can only be checked when outboard is in this position2Remove fill screw and check fluid levelFluid level should be visible in fill tube3If necessary, add Quicksilver Power Trim and Steering Fluid; or Automatic Transmission Fluid (ATF) Type F, FA or Dextron II
Tilt Angle Adjustment
MODELS WITHOUT POWER TRIM
WARNING
Operating some boats at minimum trim "In" at planing speeds will cause undesirable andor unsafe steering conditionsEach boat should be tested for handling characteristics after any adjustment is made to the tilt angleDO NOT OPERATE motor with tilt lock pin removedAdjust tilt angle of motor on transom with tilt lock pin so that anti-ventilation plate is about parallel and even with bottom of boatSpeed sometimes may be improved by tilting motor out one tilt pin hole to raise bow and reduce wetted surfaceIf motor is tilted in, boat will ride bow down, wetting more of the bottom and reducing speed, which generally will improve operation in rough waterUnder ideal conditions, efficiency is best with lower unit operating in level positionOperation with excessive tilt angle will reduce performance noticeably and may induce ventilationIt is preferable to level boat by proper loading rather than by extreme adjustment of tilt angle