1985 Mercury Outboard V-300 V-3.4L Shop Service Manual, Page 198Get this manual
BLEEDING AIR FROM POWER TRIM SYSTEM To determine if the Power Trim system contains airactivate "U p" circu it alld trim engine to the trim limi posi tion Pu sh down on lower unitIf piston ram retracts in to ydraulic cylind er more than(3 .2mm)it will be necessar to bleed air fro th Power Trim system
Bleed air from Power Trim system as follows:
Make ure thaI ma nual release va lve knob (a) is turned fuJI right (clockwise) andFill Ve ntsc rew (b) is backed oul turns (t ven the pump reservoir)
Act ivate theTraile r" circui and trim engine to fullup" positi onIf engine SlopS par t-way (lack of oil), refill pump toaddli ne (not the full line) on dipstick (b)Conti nue th is procedure until engine raises to full
"up" positi on Act iva te theDown" Cifcuit and trim engi ne to fulldownposit ionIf pump sou nd like it is un ning fre e, and the engi ne does ot trim do 'n, fill pump ilh oil to "add" line on dipstick (b) Bleed any remaining air from the trim sys tem trimming engine several limes thru entire trailering rangeEach time, engi ne is trimmed to full "down" position, fill pump with oi to "fullline on dipstick (b)ReinstallFill Ve t" screw (a) Turn screw in until sea ted then back out turns to vent the pump reservoirCheck entire trim system fo leaks