hydraullic jack plate leaking up?

[procomp]

Friend has a hydraullic jackplate on his boat and when he's running the motor moves up? He's had the cylinder checked and they said it was fine. Could an issue with the hydraullic pump cause it to leak up? Never heard of this before.
Thanks

 

[F2008]

As a test, I'd set it at a useable height, disconnect the power to the pump and then run it for a bit and see what happens. Not sure how it can move fluid without it being pumped. Perhaps an electrical issue as opposed to a hydraulic one. Not much help I know....

 

[procomp]

thanks might be worth a shot

 

[MWest77]

Air in a hydraulic system can cause funny results also.