Hard to Turn Air Bubbles in the Line

[HPLou]

I have 2 Mercruiser 4.3Lx 1989 in my boat. Each Engine as a Power Steering Pump installed but only the Starboard Engine is connected with a Belt.
At the Helm I have installed Teleflex SH-5023 Helm safe-t . I am pretty sure that is a Rotery System. When I turn the Steering Weel I can Feel Like there is Air Bubbles stock somewere in the line. I have tried filling Oil throught the Filling Tube while moving the Weel from one end to the other. After one two minutes of turning I am able to Feel a very constant mouvement (very easy) on the Steering Weel. But it does not stay that way at all. It is hard to turn again few minutes after.
I tried Searching here & on You Tube. All the info I find refers to Outboard engines.
What can cause my problem ?
What is the proper way to purge the system ?

 

[wrench 3]

For PS bleeding instructions go to http://boatinfo.no/lib/mercruiser/manuals/mercruiser7.html#/426 clear the page numbers at the bottom center of the screen and enter 427.

 

[HPLou]

Thank You wrench 3. I printed the steps to follow and will follow this week end.