Power trim pump?

Question

some say moter oil some say hyd, what would work better, my pump goes up ok but down real slow, i have changed all o rings in the pump and cleaned it all up, 165 hp mercruiser, 1976

Answer 1

Go to a Merc dealer and get the proper hydraulic fluid for the trim pump.  If that doesn't work, you might need to replace the pump.

Answer 2

My 1977 Mercury OB 150hp manual states "use only 20 weight oil only in the reservoir for the hydraulic lift."  You might want to check out the "iboats.com" Mercury OB forum for specifics on your boats motor.

Answer 3

Somehow you've gotten debris in your hydraulic line to the actuator. On both sides of the actuator are hose fittings.  Inside each one is a wire mesh screen (sometimes called a "rock-catcher".  Enough small particles or sludge can build up on these screens (especially with motor oil instead of hydro), and the flow drops dramatically.

rather than spending a lot of time diagnosing where the "large deltaP" is , I would take off the fittings at both ends of the supply hose responsible for the down movement.

if "down is accomplished by just "draining" the actuator, the this really is the sort of problem caused by a clogged screen.

from now on use only the recommended fluid and perhaps install a filter in the reservouir return line.

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