Yesterday I had a big coolant leak that lead to my car overheating. The engine started knocking and it stalled. Today after a teardown the radiator was bone dry as the plastic tank cracked. The thermostat is covered it what seems to be metal powder. What is this powder? Water Pump disintegratred? Also whats is next after a big overheat. Compression Test? Leakdown test? What else? My oil doesn't seem to have mixed with coolant and a scan reveals that my cylinder 4 misfired. Let me know. Thanks