40 hp Mariner Tilt/Trim problem

Bought a boat a few months back it has a 1996 40 hp Mariner (Mercury) and tilt/trim did not work. The electric motor was bad. Motor had been in salt water so all the bolts broke off when trying to remove tilt unit. So I found another unit off of a 60 hp mercury. Electric motor was bad so I replace it and then pressure builds up in the reservoir so I'm thinking a pump problem
So I take the pump off of the 40 hp and install it and have the same problem. I blew air into cylinder and piston works good. It' odd to have two pumps with the same problem. It will blow the fluid back at you when you remove the oil fill plug. Any thoughts on what is my problem would be appreciated.
Thanks
John.

Air in system would be my first thought,after you check the manual release valve is closed.

haventaclue said:

Air in system would be my first thought,after you check the manual release valve is closed.

Click to expand...

That was a thought I had if the piston is full of air and the reservoir is got fluid and air, how do you bleed all the air out? The manual release is closed that's just alot of air and how does it get out. I may just need the correct way to fill and bleed from totally empty.
Thanks for the suggestion. That may very well be the problem.

Tilt the engine all the way up,you might need to open the manual release,don't forget to close it again.Open and fill the reservoir to level,close and operate system up and down a couple of times,manually if you have to.Repeat until there's no need to add fluid. That should have bled the system.

Looks like I found the problem. The manual release teflon was broken off down near the tip.
So far it works fine. Thanks to everyone who helped. I'm sure this wont be my last issue.