1984 Mercury 90 HP Tilt/Trim issues

[pshipston]

I have searched a few times for this issue .. and I was not able to find a solution .. so if it is out there and I missed it .. I apologize ..

so here goes .. I bought this boat motor package may long this year .. run good .. everything works .. but this past week I have noticed that when I beech or dock my boat I tilt motor half way up or so .. and in about an hour its all way down if docked .. or on bottom if beeched .. all the research I have done has pointed me towards the fluid level ( checked and is good ) or the pressure release valve ( removed checked new o-rings re inserted ) so I am not sure where to go from here .. is it my pump itself ?? ..

and now what I have noticed in playing with my tilt trim the last couple days .. if I just raise the motor half way.. or 3/4's of the way up .. the motor will slowly lower .. but if I lift motor right to the top then lower it to 3/4's or half way down .. the motor does not slowly go down ..

Also .. when at half or WOT I am not able to trim the motor up until I remove power from the engine .then it lifts ..

so with all that said .. any and all help would be greatly appreciated ..

 

[alldodge]

if I lift motor right to the top then lower it to 3/4's or half way down .. the motor does not slowly go down

Howdy

I think your dealing with a pump and check valve leak problem. Unable to find an outboard trim system, but have found one for a Mercruiser. The system works the same its just location and size. Note item 1 the shuttle valves. They are used to seal off the ports so fluid does not leak past once the pump has stopped. If your fluid and pump channels are gunked up, these valves will not slide easy. Could try flushing with ATF and then refill with 10W30. The ATF may clean up some crud