My overflow bottle bubbles but don't empty. Raidiator loosing fluid.

bad cap -or bad head gasket.you better pray it's only the cap.

If You are a do it yourself mechanic and have plenty of time I would check the reserve alkalinity of your antifreeze with some test strips. "Acustrip" is the common one part number: 1550 www.acustrip.com or call 800-947-2078. My results indicated my antifreeze was positive for motor oil. Compare the strip to the diagram on the bottle to determine your situation. It will be obvious if it has motor oil in it and when you drain (if you do) the ANTIFREEZE you'll see the streams of oil and it will not look anything like clean transparent green or red antifreeze. You'll be able to tell and this means you need to have your cylinder head resurfaced and new head gasket and head bolts.