I really think that this new radiator is part of the reason that the tank is overflowing. It is larger than the stock one. There is no boiling that I have been able to see. On just about every vehicle I have seen the expansion tank showed evidence of overflowing coolant. I think that is why newer cars have pressureized coolant recovery tanks. This started some time in the mid 90's in think. A mechanic at Ford told me that it is not uncommon for this to occur. I just think that mine does it more so that most. Anyway, I guess I'll just have to live with it.

 

I am living with splashes, drips and drops coming out the top. You said the reservoir is empty, that is different. Don't give up on it, if you ever get the time and the extra money I would let a pro inspect the system.

 

The only time I ever had antifreeze leak out is when the freeze plugs started going. Never had it overflow and leak out my overflow tank. Maybe because the 300cid has that cooling fan. But I think it's to keep the fuel from boiling away in the fuel rail.
Mike B
88 F-150 Super Cab

 

Is this the original motor? Perhaps the resevoir is too small....
My 94 doesn't do this at all.
Popa Tim