I tried to find if anyone else has posted about this, but didnt have any luck.  Maybe I'm just bad at searching.  Anyway, I have SeaStar hydraulic steering on my 200 Yamaha, and it was very loose.  I filled at the helm and bled the line of air and it was nice and tight.  I tightened the connections to the cylinder and to the reservoir under the dash.  After sitting a week or so, I can swing the motor about 6 inches each way by hand, so clearly there's a problem.  Any suggestions?  

You need to bleed it again.  I put a new sea star system on my 225 Evinrude last year and it took longer to get the air out than the rest of the install. There was a specific sequence to bleeding the lines so I would look it up online and follow them precisely.

I had a bad seal back in january, i know bleeding the steering can be a pain in the behind, so i actually took it to a mechanic and let them do it. Did it cost more...yes, could i have done it my self...yes... but the mechanic does it all the time, it took him no time to do it..he did it right the first time and i didnt have to worry with it.