Why doesn't my radiator flush when opened?

Flush the radiator out and make sure the water is clean

We never open the petcock because something cracks inside and you'll have a leak that drips about once every ten seconds. That happened on about nine out of ten cars. We always pull the lower radiator hose off. The only fix for a leaking petcock is to replace the radiator. You may not have any damage yet. Once you turn the petcock a quarter turn, you must pull it out toward the rear of the car.