By-Pass the heater core?

A mechanic decided to by-pass my heater core, because I had a leak. I drove away from the shop to my home. The car was smoking under the hood. I left it alone, for a while. Later I just tried in my driveway no smoke. He had wasted antifreeze and water. Fixing the hoses. Next day I drove about 6 miles and parked the car. Fluid was coming from my reservoir jug, it overheated. I waited for it to cool, then returned home after adding more antifreeze and water. Today it started making a sound like its dry. I drove less than 2 miles. What's wrong, other than it's an old vehicle?