2001 Mercury Mariner 50-60HP Factory Service Manual, Page 323Get this manual
POWER TRIM
In the up mode, as the piston rod (a) extends from the cylinder (w), the memory piston (t) clears or uncovers the pressure relief passageOil from the up cavity will enter this passage and, if required, causes the tilt relief piston (s) to open the tilt pressure relief valve (r)This valve lowers the amount of pressure available to lift the outboard motorWith the engine in forward gear, and at high engine rpm, the oil pressure available will not be able to overcome the propeller thrust, limiting the trim range to below the pressure relief orificeWhen the engine rpm falls or if engine is not in forward gear, the oil pressure is available to extend the piston rod (a) up into the tilt range