1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 247Get this manual
2Install components 3Open valve (d) and close valve (e)4Install fill plug5Close Manual Release Valve (clockwise)6Run trim "DOWN"Minimum pressure should be 500 P.S.I(35 kgcm2)
7Tilt outboard full "UP" and engage tilt lock lever8Slowly remove "Fill" plug to bleed pressure9Open Manual Release Valve to turns to release any remaining pressure10Remove test gauge hose and adapter fittingInstall allen plug