[Vwdiesel] 81 Rabbit w/ a fever

[Rolf Pechukas]

hey gang
my 81 has had a leaky heater core for several months now
too cold over the winter to deal w/ it, now too busy over the summer
anyway, I was just adding coolant to keep it topped up and letting it  
leak
NOW, however, running hot even though coolant topped up
I remove res cap and steamy bubbly even though res full
what's going on?
normally I only get steam when res level low and too little coolant in  
system
is the water pump toast?

I am assuming I need to do both heater core and water pump
any other reason I might be having circulation problems?
block/clog somewhere? where might I look? how to test water pump?  
where to find procedure/illustrations?

thanks
Rolf in MA