Overheating

You need a live person to look under the hood for the source of the leak. You didn't even bother to list which engine you have. If the coolant runs out as fast as you can pour it in, the leak should be easy to find once parts like power steering pump or generator are moved out of the way. For leaks that only occur after the engine has warmed up, a pressure test will usually cause the leak to be easy to find. For real slow leaks, especially those where the coolant evaporates before hitting the ground, you can add a small bottle of dark purple dye, then search a day or two later with a black light. The dye will show up as a bright yellow stain that you can follow back to the source. Auto parts stores will have the dye, and those that rent or borrow tools will have a black light.

Based on the mileage you listed, a leaking water pump is a good suspect. Based on age, a corroded core plug is another good suspect. Both of those can leak slowly or very fast.