1987 Overheat and lose of coolant

[rwrnorman]

Loosing coolant and can't find out where it is going. Have done the bleed as instructed in the manual - rear wheels up, bleed all valves, bring up to temp, refill, bleed again, top off. Good for several days but then its gone! Checked oil - looks good, checked under carraige - no sign of fluid loose there. Doesn't appear to be coming out the exhaust. Coupe areas of concern = overflow bottle doesn't ever change quantity - always appears same. Top cap of overflow bottle is cracked - does not seal - could this be part of the problem? Bleed valve by thermostat with tube running to overflow bottle looks very rusty and not sure if its working or not. Does turn but very hard. What am I missing? Help! I don't want this car hurt its almost show quality and we love it. NEW MR2 OWERS.

Rich