using tons of engine coolant

A small crack can leak a lot of coolant. Use some Bar's if you want to plug it on the cheap, or throw a new ($60) radiator in it.

This is What I would do if I were you, 1) figure out how much coolant is being consumed and where the coolent leak is ( for example is it the reservoir leaking or is it the radiator leaking. 2) look into addressing the problem you can add some additives like stop the leak but the best option is to address the issue with either soldering the radiator or replacing it or replacing the reservoir tank Additives are not a solution to the problem they in my case caused my head gaskets to leak

Fix the freakin radiator! Avoid using stop leak.