Mercury Mariner Outboard 225 3 Litre Service Manual 1994, Page 187Get this manual
NOTE: Automatic Transmission Fluid (ATF) Type F, FA, or Dexronmay be used TO CHECK:
CAUTION
Tilt outboard to fullUp" position and engage tilt lock lever before checking fluid levelSystem is pressur IzedExtend trim and tilt rams fully to depressurize systemRemove fill plug and O-ring System is full when oil level is present at filler holeTighten fill plug securely
Hydraulic System Troubleshooting