BMW Repair: Cooling system question, condensor fins, head gasket

Question
Hello,

My name is Adlai.  I am working on a 1989 525i and I had a few questions since I am not familiar with this cooling system. The original complaint was It sounded like the water was boiling in the radiator and the gauge went into the red . Then another time it sounded like possible boiling but the gauge read normal in the middle. After both times the expansion tank was empty and had to be filled probably from boiling over. Other than those instances it was normal.The radiator fins and condensor fins look clear. I put a thermostat thinking may be it was sticking. But now I am having problems refilling it. Now I think there are other issues. I work on Toyotas so this system is different in that the expansion tank is on the radiator and you don't fill the radiator directly. I fill the tank and it doesn't go down, even with both bleeders open. And the hoses sound like they are empty. So I am wondering first where does the coolant go from the exp. tank? Does it go directly to the radiator? Or through the little hose at the base of the exp. tank to the heater core and thermostat housing? I would think that the tank would feed the the radiator and the coolant would push the air out of the bleeder. Then I tried Starting the engine and the hoses did not pressurize but I think I is because the system is not filling properly. The system has to be full except for the little bit of air still trapped to circulate. I am wondering is the radiator clogged or is there another possibilty? I hope this is enough information, but sorry the question is so long.
vin WBAHC1308K1518900
Thank you  

Answer
You have checked the fins of the radiator and the condenser which you said were fine.I believe that you must still have air in the system.Try bleeding it again.Where it has gotten hot be aware that damamge to the head gasket could have occured.Also try loosening the hose at the highest spot or at the heater core to make sure coolant is present.