1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 276Get this manual
TO PURGE: IMPORTANT: Fill plug and O-ring must be tightened securely before purging systemIMPORTANT: Run Trim System in short "jogs" until pump is primed and trim system movesIf trim motor is run without priming pump, driveshaft failure could resultCycle outboard through entire trimtilt range timesCheck fluid level after purging systemPush down on outboard when trim rams are slightly extendedIf rams retract more than 18 in(3.2 mm), air is present in systemCycle system again and check fluid levelTO CHECK:
Hydraulic System Troubleshooting
IMPORTANT: Operate Power Trim System after each check to see if problem is 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 necessary(Refer to "Fill, Check, and PurgePower Trim System") preceding3Check for external leaks in the systemReplace defective parts if leak is found4Check for air in the system and purge if necessary(Refer to "Fill, Check, and PurgePower Trim System") preceding