Mercury Mariner V-250 V-275 Outboard Service Shop Manual 1990, Page 277Get this manual
Filling and Bleeding the Power Trim System Checking Oil Level and Filling
1Position engine in full "downposition
Bleeding Air From Power Trim System
To determine jf the Power Trim system contains air, activate "Up" circuit and trim eng ine to he rim limit position Push down on lower un itIf piston ram retracts into hydraulic cylinder more than 1(3.2mm), it will be necessary to bleed air from the Power Trim system Bleed ai ro Power rim system as foHows: Make su re that manual release valve knob is turned fuJI right (clockwise) andFil llVent" screw is backed out 1-1turns (to vent the pump reservoir)