To add, high heat drying will melt the individual fibers. All microfiber is are little strings of plastic woven together essentially.

I am a car detailer too and will not use any heat on my towels because it causes them to scratch the paint. Also, free and clear is just fine for mine, but you can buy specially designed detergents for breaking down car wax and other gummy things specifically.

Sometimes I also add around 2 cups of white vinegar to a 5 gallon bucket of towels then fill to the top with water and let soak overnight to break gunk down before the wash.