1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 313Get this manual
Hydraulic System Troubleshooting Support outboard with tilt lock lever when servicing power trim systemAfter debris or failed components have been found (during troubleshooting procedures) disassemble unit completely and replace all O-ringsCheck ball valve components and castings must be cleaned using engine cleaner and compressed air or replaced prior to reassemblyPower trim system is pressurizedOutboard must be in the full UP" position (cylinder fully extended) prior to fill screw or manual release valve removalRefer to instructions following if disassembly is requiredFollow preliminary checks before proceeding to troubleshooting flow diagrams (following)
Preliminary Checks
Operate Power Trim System after each check to see if problem is correctedIf not, proceed with the next check1Check that manual release valve is tightened to full right (clockwise) position2Check trim pump fluid level with outboard in full "UP" position and fill if necessaryRefer to "Fill and Purge the Power Trim System 3Check for external leaks in Power Trim systemReplace defective part(s) if leak is found4Outboard not holding tilted position (falls to trim in position) indicates debris or defective components in trim valve assemblyClean or replace components as required5Check manual release valve for broken stem and one O-ring remaining in the release valve passage(Separate the manifold assembly from the cylinder to dislodge broken stem Install new release valve and test system6Check for nicked, deteriorated, or misplaced O-rings throughout trim system