what is normal engine cooling system pressure?

[Larry B]

Happy 2014 to all-- I have been doing a shop clean up and found some items that might be of use to others. Put them in the spare tire FREE. Back to reason for this post. Every time I start my bus( 77 MCI 5B- 8/71 non turbo) it usually spits out 1/8 cup of anti-freeze. I have been ignoring this, too many other things to fix just add antifreeze now and then. I am going to change thermostats,but first decided to check glycol pressure before draining. Installed guage and start engine. At 150 F I still have no pressure. Shut engine off and added another guage to glycol overflow. Now have a totally closed system. After about 5 minutes of engine running again I have 4PSI on both guages.Shut engine off. In a few minutes the guage on the rad side of volumn tank is back to zero but I still have 4PSI on overflow side. I even opened the main glycol fill connection to make sure there was no pressure in volumn tank. This generates a few questions.
    1-Is the little brass item in the picture some sort of pressure regulating devise?
    2- If it is a pressure reg.-- is it possible it is plumbed backwards? Lets pressure out but nothing back in.
    3- How much glycol pressure should my system be operating at? I looked through my bus maint manual, I could find nothing on glycol pressure. Detroit manual anywhere from 7 to 12 PSI 
    4- When the glycol is drained I am going to add a glycol filter and charge cartridge. I have lots of hose and fitting left over from replacing fuel hoses , can I use them on supply and return to filter?
    At present I have no glycol leaks , but it appears My engine has been operating at atmophereic pressure. If I get this engine under pressure my non leaking might change. 
     5- What would be the normal level of glycol in the volumn/surge tank? 20 x6x 6 (6"deep).  During my clean up I found a sight glass that I want to install on tank.
     Thanks   Larry B

[Larry B]

couple more pictures