The diagram is not the overflow tank; it's the reservoir on the radiator where I pour my coolant (I don't know the actual name for it). The pressure cap isn't shown. I drew the diagram myself, so it's not entirely accurate. I was illustrating a gap in the reservoir...I wanted to know if anybody knows the purpose of that gap, 'cause antifreeze gets in there. It looks like the gap was manmade/intentional...but maybe it has something to do with the coolant problem I've been having (and describing throughout this entire thread).

Anyway...I now have correct coolant levels (the radiator and overflow tank levels are correct when the engine is cool) and I'm still losing coolant after a long drive or after a series of short trips. Also, the gurgling sound still exists whenever I accelerate...yet, when considering the intake manifold issues on Bronco II's, as mentioned by mrshorty, I'm beginning to think that could be the source of the problem. I recently discovered how the intake manifold works; it establishes air-fuel mixtures. Seeing how air is involved, it is possible that air is somehow getting into the cooling system through a problem with the intake manifold. I believe this since the gurgling sound occurs whenever I accelerate, in which case more air is pumped into the air-fuel mixture and (if my assumption is correct) is also being pumped into the coolant system. Air in the coolant system could result in slight overheating of the engine, which in turn burns off some antifreeze. This subtle overheating may be why I'm losing 2-3 inches of coolant over extended periods of driving (it would be more inches if I didn't replenish it periodically). Of course, the overheating should be indicated by my temp gauge, but I've never seen it go into the red or even jumped past the midway point...then again, I'm not sure if the temp gauge is accurate in the first place. But anyway...does anybody else think that a problem with the intake manifold could be responsible for the problem with my coolant system?