Gary,

Something similar happened to me twice with an '84.  The first time, I
thought the engine was shot; the second time I knew what the problem was
immediately.  Before you do anything else, check the cap on your pressure
tank.  A small piece of debris can take up residence on the seat of the
pressure or vacuum valve within the cap and prevent them from closing
completely.  As a result, the cooling system cannot reach its correct
operating pressure and coolant gets puked out the overflow tank.

The first time it happened to me, it was a pine needle (I had told my wife I
should cut down those damn trees) which caused the malfunction.  The second
time, it was a tiny bit of paper from the liner of the cap on the antifreeze
jug I had used for years to mix coolant.

If you have the old style black pressure cap, it can be dismantled and
cleaned of the foreign particles, although it requires a delicate hand.  You
can check you cap by blowing or sucking (sucking is probably best) on the
overflow hose nipple while pressing the valve plate firmly into the cap.  It
looks weird so do it in private.  If there is something holding a valve ajar,
you will notice some air leaking.  Or, you can make life simple and just buy
a new cap.

Good luck.

Rich