1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 314Get this manual
Leak Down CheckPump and Manifold Assembly The 1993 and 1994 models listed with power trim date codes 13011 through 23288 ONLY may experience very slow trim rate (one minute or more) with the outboard drifting back down as soon as the UP trim button is releasedThis failure usually occurs when the unit is new or after or weeks of non useThe cause may be stuck spool inside the sleeve due to an oversize or hard o-ring on the spool (SERVICE BULLETIN No93-22A)