1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 230Get this manual
Hydraulic System Troubleshooting IMPORTANT: Operate Power Trim system after each check to see if problem has been correctedIf problem has not been corrected, proceed to next check1Check that manual release valve knob is tightened to full right (clockwise) position2Check trim pump fluid level and fill if necessaryRefer to "Filling and Bleeding the Power Trim System," preceding3Check for external leaks in Power Trim systemReplace defective part(s) if leak is found4Check for air in Power Trim system and bleed if necessaryRefer to "Filling and Bleeding the Power Trim System," preceding
6Disconnect trim pump motor wires, and remove starboard transom bracket from engineRefer to "Removal" instructions in "Power Trim Assembly Removal and Installation," followingSlowly remove fill screw to bleed pressure from reservoirPlace pan under manual release valve, and slowly remove valveInspect the valve and Orings for damageIf damaged component(s) are found, replace component(s) and proceed to STEP 9If damaged component(s) are not found, reinstall manual release valve and proceed to STEP 77Remove Power Trim assembly from engine; refer to "Removal" instructions in "Power Trim Assembly Removal and Installation," followingDisassemble Power Trim assembly; refer to "Trim Rod," "Tilt Ram," and "Pump Replacement," followingInspect O-rings for damageInspect check valves for debris that could cause them to remain openIf O-rings are damaged or debris is found, replace O-rings or clean debris from check valve(s), then reassemble Power Trim assembly and proceed to STEP 9If damaged O-ring(s) or debris are not found, proceed to STEP 88Replace pump assembly; refer to "Pump Replacement," following9Install Power Trim assembly andor starboard transom bracket, steering retaining nut (models with thru-tilt tube steering) and motor wires; refer to "Installation" instructions in "Power Trim Assembly Removal and Installation," following