Mercury Mariner V-250 V-275 Outboard Service Shop Manual 1990, Page 280Get this manual
Hydraulic System Troubleshooting GENERAL CHECKS
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 oi level and fill if necessaryRefer
toFilling and Bleeding the Power Trim System"See Table of Contents3Check for external leaks in Power Trim systemTighten fitting(s) or replace defect ive part(s) if leak is found 4Check for air in Power Trim system and bleed if necessaryRelerto "Fi lli ng and Bleeding the Power Trim System"See Table of Contents