Mercury Mariner 30/40 4-Stroke Outboard Service Manual 1998, Page 298Get this manual
POWER TRIM
Shock Function Return
After the engine clears the under water object, the weight of the engine will increase the oil pressure between the memory piston (t) and shock piston (u) to the level required to open the shock return valve (h)inside the shock piston, allowing the oil to bleed back through the shock piston into the down cavityIf required, additional oil will enter the down cavity through the manifold reverse suction valve (0)This will return the engine back against the memory piston (I) and into Ihe original running position