Engine tapping noise

Engine Mechanical problem 6 cyl Front Wheel Drive Automatic 215000 miles

I was pulling a trailer when my car over heated up a mountain road, I turned the heater on and the tempature gage went down. I stayed the night, the next morning when I started my car, there was this loud tapping noise in the engine. I filled my car with gas and opened the hood to check the fluid levels and saw my radiator hose had a leak. I got that repaced and dove it another 10 hours with the heater on high to keep the engine tempature down. I had the local GM garage replace the lifters, thinking this was the problem, but the load tapping noise is still there. The mechanic said the oil looked good when he had it apart. I'm from New York State and visiting my daughter in Florida.

What do you think the problem could be?